Add Basilisk

15 files changed, 10904 insertions, 0 deletions

diff --git a/application/basilisk/components/customizableui/CustomizableUI.jsm b/application/basilisk/components/customizableui/CustomizableUI.jsm
new file mode 100644
index 000000000..41deaa922
--- /dev/null
+++ b/application/basilisk/components/customizableui/CustomizableUI.jsm
@@ -0,0 +1,4409 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+this.EXPORTED_SYMBOLS = ["CustomizableUI"];
+
+const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;
+
+Cu.import("resource://gre/modules/Services.jsm");
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PanelWideWidgetTracker",
+  "resource:///modules/PanelWideWidgetTracker.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "CustomizableWidgets",
+  "resource:///modules/CustomizableWidgets.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "DeferredTask",
+  "resource://gre/modules/DeferredTask.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PrivateBrowsingUtils",
+  "resource://gre/modules/PrivateBrowsingUtils.jsm");
+XPCOMUtils.defineLazyGetter(this, "gWidgetsBundle", function() {
+  const kUrl = "chrome://browser/locale/customizableui/customizableWidgets.properties";
+  return Services.strings.createBundle(kUrl);
+});
+XPCOMUtils.defineLazyModuleGetter(this, "ShortcutUtils",
+  "resource://gre/modules/ShortcutUtils.jsm");
+XPCOMUtils.defineLazyServiceGetter(this, "gELS",
+  "@mozilla.org/eventlistenerservice;1", "nsIEventListenerService");
+XPCOMUtils.defineLazyModuleGetter(this, "LightweightThemeManager",
+                                  "resource://gre/modules/LightweightThemeManager.jsm");
+
+const kNSXUL = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
+
+const kSpecialWidgetPfx = "customizableui-special-";
+
+const kPrefCustomizationState        = "browser.uiCustomization.state";
+const kPrefCustomizationAutoAdd      = "browser.uiCustomization.autoAdd";
+const kPrefCustomizationDebug        = "browser.uiCustomization.debug";
+const kPrefDrawInTitlebar            = "browser.tabs.drawInTitlebar";
+const kPrefWebIDEInNavbar            = "devtools.webide.widget.inNavbarByDefault";
+
+const kExpectedWindowURL = "chrome://browser/content/browser.xul";
+
+/**
+ * The keys are the handlers that are fired when the event type (the value)
+ * is fired on the subview. A widget that provides a subview has the option
+ * of providing onViewShowing and onViewHiding event handlers.
+ */
+const kSubviewEvents = [
+  "ViewShowing",
+  "ViewHiding"
+];
+
+/**
+ * The current version. We can use this to auto-add new default widgets as necessary.
+ * (would be const but isn't because of testing purposes)
+ */
+var kVersion = 6;
+
+/**
+ * Buttons removed from built-ins by version they were removed. kVersion must be
+ * bumped any time a new id is added to this. Use the button id as key, and
+ * version the button is removed in as the value.  e.g. "pocket-button": 5
+ */
+var ObsoleteBuiltinButtons = {
+  "pocket-button": 6
+};
+
+/**
+ * gPalette is a map of every widget that CustomizableUI.jsm knows about, keyed
+ * on their IDs.
+ */
+var gPalette = new Map();
+
+/**
+ * gAreas maps area IDs to Sets of properties about those areas. An area is a
+ * place where a widget can be put.
+ */
+var gAreas = new Map();
+
+/**
+ * gPlacements maps area IDs to Arrays of widget IDs, indicating that the widgets
+ * are placed within that area (either directly in the area node, or in the
+ * customizationTarget of the node).
+ */
+var gPlacements = new Map();
+
+/**
+ * gFuturePlacements represent placements that will happen for areas that have
+ * not yet loaded (due to lazy-loading). This can occur when add-ons register
+ * widgets.
+ */
+var gFuturePlacements = new Map();
+
+// XXXunf Temporary. Need a nice way to abstract functions to build widgets
+//       of these types.
+var gSupportedWidgetTypes = new Set(["button", "view", "custom"]);
+
+/**
+ * gPanelsForWindow is a list of known panels in a window which we may need to close
+ * should command events fire which target them.
+ */
+var gPanelsForWindow = new WeakMap();
+
+/**
+ * gSeenWidgets remembers which widgets the user has seen for the first time
+ * before. This way, if a new widget is created, and the user has not seen it
+ * before, it can be put in its default location. Otherwise, it remains in the
+ * palette.
+ */
+var gSeenWidgets = new Set();
+
+/**
+ * gDirtyAreaCache is a set of area IDs for areas where items have been added,
+ * moved or removed at least once. This set is persisted, and is used to
+ * optimize building of toolbars in the default case where no toolbars should
+ * be "dirty".
+ */
+var gDirtyAreaCache = new Set();
+
+/**
+ * gPendingBuildAreas is a map from area IDs to map from build nodes to their
+ * existing children at the time of node registration, that are waiting
+ * for the area to be registered
+ */
+var gPendingBuildAreas = new Map();
+
+var gSavedState = null;
+var gRestoring = false;
+var gDirty = false;
+var gInBatchStack = 0;
+var gResetting = false;
+var gUndoResetting = false;
+
+/**
+ * gBuildAreas maps area IDs to actual area nodes within browser windows.
+ */
+var gBuildAreas = new Map();
+
+/**
+ * gBuildWindows is a map of windows that have registered build areas, mapped
+ * to a Set of known toolboxes in that window.
+ */
+var gBuildWindows = new Map();
+
+var gNewElementCount = 0;
+var gGroupWrapperCache = new Map();
+var gSingleWrapperCache = new WeakMap();
+var gListeners = new Set();
+
+var gUIStateBeforeReset = {
+  uiCustomizationState: null,
+  drawInTitlebar: null,
+  currentTheme: null,
+};
+
+XPCOMUtils.defineLazyGetter(this, "log", () => {
+  let scope = {};
+  Cu.import("resource://gre/modules/Console.jsm", scope);
+  let debug;
+  try {
+    debug = Services.prefs.getBoolPref(kPrefCustomizationDebug);
+  } catch (ex) {}
+  let consoleOptions = {
+    maxLogLevel: debug ? "all" : "log",
+    prefix: "CustomizableUI",
+  };
+  return new scope.ConsoleAPI(consoleOptions);
+});
+
+var CustomizableUIInternal = {
+  initialize() {
+    log.debug("Initializing");
+
+    this.addListener(this);
+    this._defineBuiltInWidgets();
+    this.loadSavedState();
+    this._introduceNewBuiltinWidgets();
+    this._markObsoleteBuiltinButtonsSeen();
+
+    /**
+     * Please be advised that adding items to the panel by default could
+     * cause CART talos test regressions. This might happen when the
+     * number of items in the panel causes the area to become "scrollable"
+     * during the last phases of the transition. See bug 1230671 for an
+     * example of this. Be sure that what you're adding really needs to go
+     * into the panel by default, and if it does, consider swapping
+     * something out for it.
+     */
+    let panelPlacements = [
+      "edit-controls",
+      "zoom-controls",
+      "new-window-button",
+      "privatebrowsing-button",
+      "save-page-button",
+      "print-button",
+      "history-panelmenu",
+      "fullscreen-button",
+      "find-button",
+      "preferences-button",
+      "add-ons-button",
+      "sync-button",
+    ];
+
+#ifndef MOZ_DEV_EDITION
+    panelPlacements.splice(-1, 0, "developer-button");
+#endif
+
+#ifdef E10S_TESTING_ONLY
+    if (gPalette.has("e10s-button")) {
+      let newWindowIndex = panelPlacements.indexOf("new-window-button");
+      if (newWindowIndex > -1) {
+        panelPlacements.splice(newWindowIndex + 1, 0, "e10s-button");
+      }
+    }
+#endif
+
+    let showCharacterEncoding = Services.prefs.getComplexValue(
+      "browser.menu.showCharacterEncoding",
+      Ci.nsIPrefLocalizedString
+    ).data;
+    if (showCharacterEncoding == "true") {
+      panelPlacements.push("characterencoding-button");
+    }
+
+#ifdef NIGHTLY_BUILD
+    if (Services.prefs.getBoolPref("extensions.webcompat-reporter.enabled")) {
+      panelPlacements.push("webcompat-reporter-button");
+    }
+#endif
+
+    this.registerArea(CustomizableUI.AREA_PANEL, {
+      anchor: "PanelUI-menu-button",
+      type: CustomizableUI.TYPE_MENU_PANEL,
+      defaultPlacements: panelPlacements
+    }, true);
+    PanelWideWidgetTracker.init();
+
+    let navbarPlacements = [
+      "urlbar-container",
+      "search-container",
+      "bookmarks-menu-button",
+      "downloads-button",
+      "home-button",
+    ];
+
+#ifdef MOZ_DEV_EDITION
+    navbarPlacements.splice(2, 0, "developer-button");
+#endif
+
+    if (Services.prefs.getBoolPref(kPrefWebIDEInNavbar)) {
+      navbarPlacements.push("webide-button");
+    }
+
+    // Place this last, when createWidget is called for pocket, it will
+    // append to the toolbar.
+    if (Services.prefs.getPrefType("extensions.pocket.enabled") != Services.prefs.PREF_INVALID &&
+        Services.prefs.getBoolPref("extensions.pocket.enabled")) {
+        navbarPlacements.push("pocket-button");
+    }
+
+    this.registerArea(CustomizableUI.AREA_NAVBAR, {
+      legacy: true,
+      type: CustomizableUI.TYPE_TOOLBAR,
+      overflowable: true,
+      defaultPlacements: navbarPlacements,
+      defaultCollapsed: false,
+    }, true);
+
+#ifdef MENUBAR_CAN_AUTOHIDE
+    this.registerArea(CustomizableUI.AREA_MENUBAR, {
+      legacy: true,
+      type: CustomizableUI.TYPE_TOOLBAR,
+      defaultPlacements: [
+        "menubar-items",
+      ],
+      defaultCollapsed: true,
+    }, true);
+#endif
+
+    this.registerArea(CustomizableUI.AREA_TABSTRIP, {
+      legacy: true,
+      type: CustomizableUI.TYPE_TOOLBAR,
+      defaultPlacements: [
+        "tabbrowser-tabs",
+        "new-tab-button",
+        "alltabs-button",
+      ],
+      defaultCollapsed: null,
+    }, true);
+    this.registerArea(CustomizableUI.AREA_BOOKMARKS, {
+      legacy: true,
+      type: CustomizableUI.TYPE_TOOLBAR,
+      defaultPlacements: [
+        "personal-bookmarks",
+      ],
+      defaultCollapsed: true,
+    }, true);
+
+    this.registerArea(CustomizableUI.AREA_ADDONBAR, {
+      type: CustomizableUI.TYPE_TOOLBAR,
+      legacy: true,
+      defaultPlacements: ["addonbar-closebutton", "status-bar"],
+      defaultCollapsed: false,
+    }, true);
+  },
+
+  get _builtinToolbars() {
+    let toolbars = new Set([
+      CustomizableUI.AREA_NAVBAR,
+      CustomizableUI.AREA_BOOKMARKS,
+      CustomizableUI.AREA_TABSTRIP,
+      CustomizableUI.AREA_ADDONBAR,
+    ]);
+#ifndef XP_MACOSX
+    toolbars.add(CustomizableUI.AREA_MENUBAR);
+#endif
+    return toolbars;
+  },
+
+  _defineBuiltInWidgets() {
+    for (let widgetDefinition of CustomizableWidgets) {
+      this.createBuiltinWidget(widgetDefinition);
+    }
+  },
+
+  _introduceNewBuiltinWidgets() {
+    // We should still enter even if gSavedState.currentVersion >= kVersion
+    // because the per-widget pref facility is independent of versioning.
+    if (!gSavedState) {
+      // Flip all the prefs so we don't try to re-introduce later:
+      for (let [, widget] of gPalette) {
+        if (widget.defaultArea && widget._introducedInVersion === "pref") {
+          let prefId = "browser.toolbarbuttons.introduced." + widget.id;
+          Services.prefs.setBoolPref(prefId, true);
+        }
+      }
+      return;
+    }
+
+    let currentVersion = gSavedState.currentVersion;
+    for (let [id, widget] of gPalette) {
+      if (widget.defaultArea) {
+        let shouldAdd = false;
+        let shouldSetPref = false;
+        let prefId = "browser.toolbarbuttons.introduced." + widget.id;
+        if (widget._introducedInVersion === "pref") {
+          try {
+            shouldAdd = !Services.prefs.getBoolPref(prefId);
+          } catch (ex) {
+            // Pref doesn't exist:
+            shouldAdd = true;
+          }
+          shouldSetPref = shouldAdd;
+        } else if (widget._introducedInVersion > currentVersion) {
+          shouldAdd = true;
+        }
+
+        if (shouldAdd) {
+          let futurePlacements = gFuturePlacements.get(widget.defaultArea);
+          if (futurePlacements) {
+            futurePlacements.add(id);
+          } else {
+            gFuturePlacements.set(widget.defaultArea, new Set([id]));
+          }
+          if (shouldSetPref) {
+            Services.prefs.setBoolPref(prefId, true);
+          }
+        }
+      }
+    }
+
+    if (currentVersion < 2) {
+      // Nuke the old 'loop-call-button' out of orbit.
+      CustomizableUI.removeWidgetFromArea("loop-call-button");
+    }
+
+    if (currentVersion < 4) {
+      CustomizableUI.removeWidgetFromArea("loop-button-throttled");
+    }
+  },
+
+  /**
+   * _markObsoleteBuiltinButtonsSeen
+   * when upgrading, ensure obsoleted buttons are in seen state.
+   */
+  _markObsoleteBuiltinButtonsSeen() {
+    if (!gSavedState)
+      return;
+    let currentVersion = gSavedState.currentVersion;
+    if (currentVersion >= kVersion)
+      return;
+    // we're upgrading, update state if necessary
+    for (let id in ObsoleteBuiltinButtons) {
+      let version = ObsoleteBuiltinButtons[id]
+      if (version == kVersion) {
+        gSeenWidgets.add(id);
+        gDirty = true;
+      }
+    }
+  },
+
+  _placeNewDefaultWidgetsInArea(aArea) {
+    let futurePlacedWidgets = gFuturePlacements.get(aArea);
+    let savedPlacements = gSavedState && gSavedState.placements && gSavedState.placements[aArea];
+    let defaultPlacements = gAreas.get(aArea).get("defaultPlacements");
+    if (!savedPlacements || !savedPlacements.length || !futurePlacedWidgets || !defaultPlacements ||
+        !defaultPlacements.length) {
+      return;
+    }
+    let defaultWidgetIndex = -1;
+
+    for (let widgetId of futurePlacedWidgets) {
+      let widget = gPalette.get(widgetId);
+      if (!widget || widget.source !== CustomizableUI.SOURCE_BUILTIN ||
+          !widget.defaultArea || !widget._introducedInVersion ||
+          savedPlacements.indexOf(widget.id) !== -1) {
+        continue;
+      }
+      defaultWidgetIndex = defaultPlacements.indexOf(widget.id);
+      if (defaultWidgetIndex === -1) {
+        continue;
+      }
+      // Now we know that this widget should be here by default, was newly introduced,
+      // and we have a saved state to insert into, and a default state to work off of.
+      // Try introducing after widgets that come before it in the default placements:
+      for (let i = defaultWidgetIndex; i >= 0; i--) {
+        // Special case: if the defaults list this widget as coming first, insert at the beginning:
+        if (i === 0 && i === defaultWidgetIndex) {
+          savedPlacements.splice(0, 0, widget.id);
+          // Before you ask, yes, deleting things inside a let x of y loop where y is a Set is
+          // safe, and we won't skip any items.
+          futurePlacedWidgets.delete(widget.id);
+          gDirty = true;
+          break;
+        }
+        // Otherwise, if we're somewhere other than the beginning, check if the previous
+        // widget is in the saved placements.
+        if (i) {
+          let previousWidget = defaultPlacements[i - 1];
+          let previousWidgetIndex = savedPlacements.indexOf(previousWidget);
+          if (previousWidgetIndex != -1) {
+            savedPlacements.splice(previousWidgetIndex + 1, 0, widget.id);
+            futurePlacedWidgets.delete(widget.id);
+            gDirty = true;
+            break;
+          }
+        }
+      }
+      // The loop above either inserts the item or doesn't - either way, we can get away
+      // with doing nothing else now; if the item remains in gFuturePlacements, we'll
+      // add it at the end in restoreStateForArea.
+    }
+    this.saveState();
+  },
+
+  wrapWidget(aWidgetId) {
+    if (gGroupWrapperCache.has(aWidgetId)) {
+      return gGroupWrapperCache.get(aWidgetId);
+    }
+
+    let provider = this.getWidgetProvider(aWidgetId);
+    if (!provider) {
+      return null;
+    }
+
+    if (provider == CustomizableUI.PROVIDER_API) {
+      let widget = gPalette.get(aWidgetId);
+      if (!widget.wrapper) {
+        widget.wrapper = new WidgetGroupWrapper(widget);
+        gGroupWrapperCache.set(aWidgetId, widget.wrapper);
+      }
+      return widget.wrapper;
+    }
+
+    // PROVIDER_SPECIAL gets treated the same as PROVIDER_XUL.
+    let wrapper = new XULWidgetGroupWrapper(aWidgetId);
+    gGroupWrapperCache.set(aWidgetId, wrapper);
+    return wrapper;
+  },
+
+  registerArea(aName, aProperties, aInternalCaller) {
+    if (typeof aName != "string" || !/^[a-z0-9-_]{1,}$/i.test(aName)) {
+      throw new Error("Invalid area name");
+    }
+
+    let areaIsKnown = gAreas.has(aName);
+    let props = areaIsKnown ? gAreas.get(aName) : new Map();
+    const kImmutableProperties = new Set(["type", "legacy", "overflowable"]);
+    for (let key in aProperties) {
+      if (areaIsKnown && kImmutableProperties.has(key) &&
+          props.get(key) != aProperties[key]) {
+        throw new Error("An area cannot change the property for '" + key + "'");
+      }
+      // XXXgijs for special items, we need to make sure they have an appropriate ID
+      // so we aren't perpetually in a non-default state:
+      if (key == "defaultPlacements" && Array.isArray(aProperties[key])) {
+        props.set(key, aProperties[key].map(x => this.isSpecialWidget(x) ? this.ensureSpecialWidgetId(x) : x ));
+      } else {
+        props.set(key, aProperties[key]);
+      }
+    }
+    // Default to a toolbar:
+    if (!props.has("type")) {
+      props.set("type", CustomizableUI.TYPE_TOOLBAR);
+    }
+    if (props.get("type") == CustomizableUI.TYPE_TOOLBAR) {
+      // Check aProperties instead of props because this check is only interested
+      // in the passed arguments, not the state of a potentially pre-existing area.
+      if (!aInternalCaller && aProperties["defaultCollapsed"]) {
+        throw new Error("defaultCollapsed is only allowed for default toolbars.")
+      }
+      if (!props.has("defaultCollapsed")) {
+        props.set("defaultCollapsed", true);
+      }
+    } else if (props.has("defaultCollapsed")) {
+      throw new Error("defaultCollapsed only applies for TYPE_TOOLBAR areas.");
+    }
+    // Sanity check type:
+    let allTypes = [CustomizableUI.TYPE_TOOLBAR, CustomizableUI.TYPE_MENU_PANEL];
+    if (allTypes.indexOf(props.get("type")) == -1) {
+      throw new Error("Invalid area type " + props.get("type"));
+    }
+
+    // And to no placements:
+    if (!props.has("defaultPlacements")) {
+      props.set("defaultPlacements", []);
+    }
+    // Sanity check default placements array:
+    if (!Array.isArray(props.get("defaultPlacements"))) {
+      throw new Error("Should provide an array of default placements");
+    }
+
+    if (!areaIsKnown) {
+      gAreas.set(aName, props);
+
+      // Reconcile new default widgets. Have to do this before we start restoring things.
+      this._placeNewDefaultWidgetsInArea(aName);
+
+      if (props.get("legacy") && !gPlacements.has(aName)) {
+        // Guarantee this area exists in gFuturePlacements, to avoid checking it in
+        // various places elsewhere.
+        if (!gFuturePlacements.has(aName)) {
+          gFuturePlacements.set(aName, new Set());
+        }
+      } else {
+        this.restoreStateForArea(aName);
+      }
+
+      // If we have pending build area nodes, register all of them
+      if (gPendingBuildAreas.has(aName)) {
+        let pendingNodes = gPendingBuildAreas.get(aName);
+        for (let [pendingNode, existingChildren] of pendingNodes) {
+          this.registerToolbarNode(pendingNode, existingChildren);
+        }
+        gPendingBuildAreas.delete(aName);
+      }
+    }
+  },
+
+  unregisterArea(aName, aDestroyPlacements) {
+    if (typeof aName != "string" || !/^[a-z0-9-_]{1,}$/i.test(aName)) {
+      throw new Error("Invalid area name");
+    }
+    if (!gAreas.has(aName) && !gPlacements.has(aName)) {
+      throw new Error("Area not registered");
+    }
+
+    // Move all the widgets out
+    this.beginBatchUpdate();
+    try {
+      let placements = gPlacements.get(aName);
+      if (placements) {
+        // Need to clone this array so removeWidgetFromArea doesn't modify it
+        placements = [...placements];
+        placements.forEach(this.removeWidgetFromArea, this);
+      }
+
+      // Delete all remaining traces.
+      gAreas.delete(aName);
+      // Only destroy placements when necessary:
+      if (aDestroyPlacements) {
+        gPlacements.delete(aName);
+      } else {
+        // Otherwise we need to re-set them, as removeFromArea will have emptied
+        // them out:
+        gPlacements.set(aName, placements);
+      }
+      gFuturePlacements.delete(aName);
+      let existingAreaNodes = gBuildAreas.get(aName);
+      if (existingAreaNodes) {
+        for (let areaNode of existingAreaNodes) {
+          this.notifyListeners("onAreaNodeUnregistered", aName, areaNode.customizationTarget,
+                               CustomizableUI.REASON_AREA_UNREGISTERED);
+        }
+      }
+      gBuildAreas.delete(aName);
+    } finally {
+      this.endBatchUpdate(true);
+    }
+  },
+
+  registerToolbarNode(aToolbar, aExistingChildren) {
+    let area = aToolbar.id;
+    if (gBuildAreas.has(area) && gBuildAreas.get(area).has(aToolbar)) {
+      return;
+    }
+    let areaProperties = gAreas.get(area);
+
+    // If this area is not registered, try to do it automatically:
+    if (!areaProperties) {
+      // If there's no defaultset attribute and this isn't a legacy extra toolbar,
+      // we assume that we should wait for registerArea to be called:
+      if (!aToolbar.hasAttribute("defaultset") &&
+          !aToolbar.hasAttribute("customindex")) {
+        if (!gPendingBuildAreas.has(area)) {
+          gPendingBuildAreas.set(area, new Map());
+        }
+        let pendingNodes = gPendingBuildAreas.get(area);
+        pendingNodes.set(aToolbar, aExistingChildren);
+        return;
+      }
+      let props = {type: CustomizableUI.TYPE_TOOLBAR, legacy: true};
+      let defaultsetAttribute = aToolbar.getAttribute("defaultset") || "";
+      props.defaultPlacements = defaultsetAttribute.split(",").filter(s => s);
+      this.registerArea(area, props);
+      areaProperties = gAreas.get(area);
+    }
+
+    this.beginBatchUpdate();
+    try {
+      let placements = gPlacements.get(area);
+      if (!placements && areaProperties.has("legacy")) {
+        let legacyState = aToolbar.getAttribute("currentset");
+        if (legacyState) {
+          legacyState = legacyState.split(",").filter(s => s);
+        }
+
+        // Manually restore the state here, so the legacy state can be converted.
+        this.restoreStateForArea(area, legacyState);
+        placements = gPlacements.get(area);
+      }
+
+      // Check that the current children and the current placements match. If
+      // not, mark it as dirty:
+      if (aExistingChildren.length != placements.length ||
+          aExistingChildren.every((id, i) => id == placements[i])) {
+        gDirtyAreaCache.add(area);
+      }
+
+      if (areaProperties.has("overflowable")) {
+        aToolbar.overflowable = new OverflowableToolbar(aToolbar);
+      }
+
+      this.registerBuildArea(area, aToolbar);
+
+      // We only build the toolbar if it's been marked as "dirty". Dirty means
+      // one of the following things:
+      // 1) Items have been added, moved or removed from this toolbar before.
+      // 2) The number of children of the toolbar does not match the length of
+      //    the placements array for that area.
+      //
+      // This notion of being "dirty" is stored in a cache which is persisted
+      // in the saved state.
+      if (gDirtyAreaCache.has(area)) {
+        this.buildArea(area, placements, aToolbar);
+      }
+      this.notifyListeners("onAreaNodeRegistered", area, aToolbar.customizationTarget);
+      aToolbar.setAttribute("currentset", placements.join(","));
+    } finally {
+      this.endBatchUpdate();
+    }
+  },
+
+  buildArea(aArea, aPlacements, aAreaNode) {
+    let document = aAreaNode.ownerDocument;
+    let window = document.defaultView;
+    let inPrivateWindow = PrivateBrowsingUtils.isWindowPrivate(window);
+    let container = aAreaNode.customizationTarget;
+    let areaIsPanel = gAreas.get(aArea).get("type") == CustomizableUI.TYPE_MENU_PANEL;
+
+    if (!container) {
+      throw new Error("Expected area " + aArea
+                      + " to have a customizationTarget attribute.");
+    }
+
+    // Restore nav-bar visibility since it may have been hidden
+    // through a migration path (bug 938980) or an add-on.
+    if (aArea == CustomizableUI.AREA_NAVBAR) {
+      aAreaNode.collapsed = false;
+    }
+
+    this.beginBatchUpdate();
+
+    try {
+      let currentNode = container.firstChild;
+      let placementsToRemove = new Set();
+      for (let id of aPlacements) {
+        while (currentNode && currentNode.getAttribute("skipintoolbarset") == "true") {
+          currentNode = currentNode.nextSibling;
+        }
+
+        if (currentNode && currentNode.id == id) {
+          currentNode = currentNode.nextSibling;
+          continue;
+        }
+
+        if (this.isSpecialWidget(id) && areaIsPanel) {
+          placementsToRemove.add(id);
+          continue;
+        }
+
+        let [provider, node] = this.getWidgetNode(id, window);
+        if (!node) {
+          log.debug("Unknown widget: " + id);
+          continue;
+        }
+
+        let widget = null;
+        // If the placements have items in them which are (now) no longer removable,
+        // we shouldn't be moving them:
+        if (provider == CustomizableUI.PROVIDER_API) {
+          widget = gPalette.get(id);
+          if (!widget.removable && aArea != widget.defaultArea) {
+            placementsToRemove.add(id);
+            continue;
+          }
+        } else if (provider == CustomizableUI.PROVIDER_XUL &&
+                   node.parentNode != container && !this.isWidgetRemovable(node)) {
+          placementsToRemove.add(id);
+          continue;
+        } // Special widgets are always removable, so no need to check them
+
+        if (inPrivateWindow && widget && !widget.showInPrivateBrowsing) {
+          continue;
+        }
+
+        this.ensureButtonContextMenu(node, aAreaNode);
+        if (node.localName == "toolbarbutton") {
+          if (areaIsPanel) {
+            node.setAttribute("wrap", "true");
+          } else {
+            node.removeAttribute("wrap");
+          }
+        }
+
+        // This needs updating in case we're resetting / undoing a reset.
+        if (widget) {
+          widget.currentArea = aArea;
+        }
+        this.insertWidgetBefore(node, currentNode, container, aArea);
+        if (gResetting) {
+          this.notifyListeners("onWidgetReset", node, container);
+        } else if (gUndoResetting) {
+          this.notifyListeners("onWidgetUndoMove", node, container);
+        }
+      }
+
+      if (currentNode) {
+        let palette = aAreaNode.toolbox ? aAreaNode.toolbox.palette : null;
+        let limit = currentNode.previousSibling;
+        let node = container.lastChild;
+        while (node && node != limit) {
+          let previousSibling = node.previousSibling;
+          // Nodes opt-in to removability. If they're removable, and we haven't
+          // seen them in the placements array, then we toss them into the palette
+          // if one exists. If no palette exists, we just remove the node. If the
+          // node is not removable, we leave it where it is. However, we can only
+          // safely touch elements that have an ID - both because we depend on
+          // IDs, and because such elements are not intended to be widgets
+          // (eg, titlebar-placeholder elements).
+          if (node.id && node.getAttribute("skipintoolbarset") != "true") {
+            if (this.isWidgetRemovable(node)) {
+              if (palette && !this.isSpecialWidget(node.id)) {
+                palette.appendChild(node);
+                this.removeLocationAttributes(node);
+              } else {
+                container.removeChild(node);
+              }
+            } else {
+              node.setAttribute("removable", false);
+              log.debug("Adding non-removable widget to placements of " + aArea + ": " +
+                        node.id);
+              gPlacements.get(aArea).push(node.id);
+              gDirty = true;
+            }
+          }
+          node = previousSibling;
+        }
+      }
+
+      // If there are placements in here which aren't removable from their original area,
+      // we remove them from this area's placement array. They will (have) be(en) added
+      // to their original area's placements array in the block above this one.
+      if (placementsToRemove.size) {
+        let placementAry = gPlacements.get(aArea);
+        for (let id of placementsToRemove) {
+          let index = placementAry.indexOf(id);
+          placementAry.splice(index, 1);
+        }
+      }
+
+      if (gResetting) {
+        this.notifyListeners("onAreaReset", aArea, container);
+      }
+    } finally {
+      this.endBatchUpdate();
+    }
+  },
+
+  addPanelCloseListeners(aPanel) {
+    gELS.addSystemEventListener(aPanel, "click", this, false);
+    gELS.addSystemEventListener(aPanel, "keypress", this, false);
+    let win = aPanel.ownerGlobal;
+    if (!gPanelsForWindow.has(win)) {
+      gPanelsForWindow.set(win, new Set());
+    }
+    gPanelsForWindow.get(win).add(this._getPanelForNode(aPanel));
+  },
+
+  removePanelCloseListeners(aPanel) {
+    gELS.removeSystemEventListener(aPanel, "click", this, false);
+    gELS.removeSystemEventListener(aPanel, "keypress", this, false);
+    let win = aPanel.ownerGlobal;
+    let panels = gPanelsForWindow.get(win);
+    if (panels) {
+      panels.delete(this._getPanelForNode(aPanel));
+    }
+  },
+
+  ensureButtonContextMenu(aNode, aAreaNode) {
+    const kPanelItemContextMenu = "customizationPanelItemContextMenu";
+
+    let currentContextMenu = aNode.getAttribute("context") ||
+                             aNode.getAttribute("contextmenu");
+    let place = CustomizableUI.getPlaceForItem(aAreaNode);
+    let contextMenuForPlace = place == "panel" ?
+                                kPanelItemContextMenu :
+                                null;
+    if (contextMenuForPlace && !currentContextMenu) {
+      aNode.setAttribute("context", contextMenuForPlace);
+    } else if (currentContextMenu == kPanelItemContextMenu &&
+               contextMenuForPlace != kPanelItemContextMenu) {
+      aNode.removeAttribute("context");
+      aNode.removeAttribute("contextmenu");
+    }
+  },
+
+  getWidgetProvider(aWidgetId) {
+    if (this.isSpecialWidget(aWidgetId)) {
+      return CustomizableUI.PROVIDER_SPECIAL;
+    }
+    if (gPalette.has(aWidgetId)) {
+      return CustomizableUI.PROVIDER_API;
+    }
+    // If this was an API widget that was destroyed, return null:
+    if (gSeenWidgets.has(aWidgetId)) {
+      return null;
+    }
+
+    // We fall back to the XUL provider, but we don't know for sure (at this
+    // point) whether it exists there either. So the API is technically lying.
+    // Ideally, it would be able to return an error value (or throw an
+    // exception) if it really didn't exist. Our code calling this function
+    // handles that fine, but this is a public API.
+    return CustomizableUI.PROVIDER_XUL;
+  },
+
+  getWidgetNode(aWidgetId, aWindow) {
+    let document = aWindow.document;
+
+    if (this.isSpecialWidget(aWidgetId)) {
+      let widgetNode = document.getElementById(aWidgetId) ||
+                       this.createSpecialWidget(aWidgetId, document);
+      return [ CustomizableUI.PROVIDER_SPECIAL, widgetNode];
+    }
+
+    let widget = gPalette.get(aWidgetId);
+    if (widget) {
+      // If we have an instance of this widget already, just use that.
+      if (widget.instances.has(document)) {
+        log.debug("An instance of widget " + aWidgetId + " already exists in this "
+                  + "document. Reusing.");
+        return [ CustomizableUI.PROVIDER_API,
+                 widget.instances.get(document) ];
+      }
+
+      return [ CustomizableUI.PROVIDER_API,
+               this.buildWidget(document, widget) ];
+    }
+
+    log.debug("Searching for " + aWidgetId + " in toolbox.");
+    let node = this.findWidgetInWindow(aWidgetId, aWindow);
+    if (node) {
+      return [ CustomizableUI.PROVIDER_XUL, node ];
+    }
+
+    log.debug("No node for " + aWidgetId + " found.");
+    return [null, null];
+  },
+
+  registerMenuPanel(aPanelContents) {
+    if (gBuildAreas.has(CustomizableUI.AREA_PANEL) &&
+        gBuildAreas.get(CustomizableUI.AREA_PANEL).has(aPanelContents)) {
+      return;
+    }
+
+    let document = aPanelContents.ownerDocument;
+
+    aPanelContents.toolbox = document.getElementById("navigator-toolbox");
+    aPanelContents.customizationTarget = aPanelContents;
+
+    this.addPanelCloseListeners(this._getPanelForNode(aPanelContents));
+
+    let placements = gPlacements.get(CustomizableUI.AREA_PANEL);
+    this.buildArea(CustomizableUI.AREA_PANEL, placements, aPanelContents);
+    this.notifyListeners("onAreaNodeRegistered", CustomizableUI.AREA_PANEL, aPanelContents);
+
+    for (let child of aPanelContents.children) {
+      if (child.localName != "toolbarbutton") {
+        if (child.localName == "toolbaritem") {
+          this.ensureButtonContextMenu(child, aPanelContents);
+        }
+        continue;
+      }
+      this.ensureButtonContextMenu(child, aPanelContents);
+      child.setAttribute("wrap", "true");
+    }
+
+    this.registerBuildArea(CustomizableUI.AREA_PANEL, aPanelContents);
+  },
+
+  onWidgetAdded(aWidgetId, aArea, aPosition) {
+    this.insertNode(aWidgetId, aArea, aPosition, true);
+
+    if (!gResetting) {
+      this._clearPreviousUIState();
+    }
+  },
+
+  onWidgetRemoved(aWidgetId, aArea) {
+    let areaNodes = gBuildAreas.get(aArea);
+    if (!areaNodes) {
+      return;
+    }
+
+    let area = gAreas.get(aArea);
+    let isToolbar = area.get("type") == CustomizableUI.TYPE_TOOLBAR;
+    let isOverflowable = isToolbar && area.get("overflowable");
+    let showInPrivateBrowsing = gPalette.has(aWidgetId)
+                              ? gPalette.get(aWidgetId).showInPrivateBrowsing
+                              : true;
+
+    for (let areaNode of areaNodes) {
+      let window = areaNode.ownerGlobal;
+      if (!showInPrivateBrowsing &&
+          PrivateBrowsingUtils.isWindowPrivate(window)) {
+        continue;
+      }
+
+      let container = areaNode.customizationTarget;
+      let widgetNode = window.document.getElementById(aWidgetId);
+      if (widgetNode && isOverflowable) {
+        container = areaNode.overflowable.getContainerFor(widgetNode);
+      }
+
+      if (!widgetNode || !container.contains(widgetNode)) {
+        log.info("Widget " + aWidgetId + " not found, unable to remove from " + aArea);
+        continue;
+      }
+
+      this.notifyListeners("onWidgetBeforeDOMChange", widgetNode, null, container, true);
+
+      // We remove location attributes here to make sure they're gone too when a
+      // widget is removed from a toolbar to the palette. See bug 930950.
+      this.removeLocationAttributes(widgetNode);
+      // We also need to remove the panel context menu if it's there:
+      this.ensureButtonContextMenu(widgetNode);
+      widgetNode.removeAttribute("wrap");
+      if (gPalette.has(aWidgetId) || this.isSpecialWidget(aWidgetId)) {
+        container.removeChild(widgetNode);
+      } else {
+        areaNode.toolbox.palette.appendChild(widgetNode);
+      }
+      this.notifyListeners("onWidgetAfterDOMChange", widgetNode, null, container, true);
+
+      if (isToolbar) {
+        areaNode.setAttribute("currentset", gPlacements.get(aArea).join(","));
+      }
+
+      let windowCache = gSingleWrapperCache.get(window);
+      if (windowCache) {
+        windowCache.delete(aWidgetId);
+      }
+    }
+    if (!gResetting) {
+      this._clearPreviousUIState();
+    }
+  },
+
+  onWidgetMoved(aWidgetId, aArea, aOldPosition, aNewPosition) {
+    this.insertNode(aWidgetId, aArea, aNewPosition);
+    if (!gResetting) {
+      this._clearPreviousUIState();
+    }
+  },
+
+  onCustomizeEnd(aWindow) {
+    this._clearPreviousUIState();
+  },
+
+  registerBuildArea(aArea, aNode) {
+    // We ensure that the window is registered to have its customization data
+    // cleaned up when unloading.
+    let window = aNode.ownerGlobal;
+    if (window.closed) {
+      return;
+    }
+    this.registerBuildWindow(window);
+
+    // Also register this build area's toolbox.
+    if (aNode.toolbox) {
+      gBuildWindows.get(window).add(aNode.toolbox);
+    }
+
+    if (!gBuildAreas.has(aArea)) {
+      gBuildAreas.set(aArea, new Set());
+    }
+
+    gBuildAreas.get(aArea).add(aNode);
+
+    // Give a class to all customize targets to be used for styling in Customize Mode
+    let customizableNode = this.getCustomizeTargetForArea(aArea, window);
+    customizableNode.classList.add("customization-target");
+  },
+
+  registerBuildWindow(aWindow) {
+    if (!gBuildWindows.has(aWindow)) {
+      gBuildWindows.set(aWindow, new Set());
+
+      aWindow.addEventListener("unload", this);
+      aWindow.addEventListener("command", this, true);
+
+      this.notifyListeners("onWindowOpened", aWindow);
+    }
+  },
+
+  unregisterBuildWindow(aWindow) {
+    aWindow.removeEventListener("unload", this);
+    aWindow.removeEventListener("command", this, true);
+    gPanelsForWindow.delete(aWindow);
+    gBuildWindows.delete(aWindow);
+    gSingleWrapperCache.delete(aWindow);
+    let document = aWindow.document;
+
+    for (let [areaId, areaNodes] of gBuildAreas) {
+      let areaProperties = gAreas.get(areaId);
+      for (let node of areaNodes) {
+        if (node.ownerDocument == document) {
+          this.notifyListeners("onAreaNodeUnregistered", areaId, node.customizationTarget,
+                               CustomizableUI.REASON_WINDOW_CLOSED);
+          if (areaProperties.has("overflowable")) {
+            node.overflowable.uninit();
+            node.overflowable = null;
+          }
+          areaNodes.delete(node);
+        }
+      }
+    }
+
+    for (let [, widget] of gPalette) {
+      widget.instances.delete(document);
+      this.notifyListeners("onWidgetInstanceRemoved", widget.id, document);
+    }
+
+    for (let [, areaMap] of gPendingBuildAreas) {
+      let toDelete = [];
+      for (let [areaNode, ] of areaMap) {
+        if (areaNode.ownerDocument == document) {
+          toDelete.push(areaNode);
+        }
+      }
+      for (let areaNode of toDelete) {
+        areaMap.delete(areaNode);
+      }
+    }
+
+    this.notifyListeners("onWindowClosed", aWindow);
+  },
+
+  setLocationAttributes(aNode, aArea) {
+    let props = gAreas.get(aArea);
+    if (!props) {
+      throw new Error("Expected area " + aArea + " to have a properties Map " +
+                      "associated with it.");
+    }
+
+    aNode.setAttribute("cui-areatype", props.get("type") || "");
+    let anchor = props.get("anchor");
+    if (anchor) {
+      aNode.setAttribute("cui-anchorid", anchor);
+    } else {
+      aNode.removeAttribute("cui-anchorid");
+    }
+  },
+
+  removeLocationAttributes(aNode) {
+    aNode.removeAttribute("cui-areatype");
+    aNode.removeAttribute("cui-anchorid");
+  },
+
+  insertNode(aWidgetId, aArea, aPosition, isNew) {
+    let areaNodes = gBuildAreas.get(aArea);
+    if (!areaNodes) {
+      return;
+    }
+
+    let placements = gPlacements.get(aArea);
+    if (!placements) {
+      log.error("Could not find any placements for " + aArea +
+                " when moving a widget.");
+      return;
+    }
+
+    // Go through each of the nodes associated with this area and move the
+    // widget to the requested location.
+    for (let areaNode of areaNodes) {
+      this.insertNodeInWindow(aWidgetId, areaNode, isNew);
+    }
+  },
+
+  insertNodeInWindow(aWidgetId, aAreaNode, isNew) {
+    let window = aAreaNode.ownerGlobal;
+    let showInPrivateBrowsing = gPalette.has(aWidgetId)
+                              ? gPalette.get(aWidgetId).showInPrivateBrowsing
+                              : true;
+
+    if (!showInPrivateBrowsing && PrivateBrowsingUtils.isWindowPrivate(window)) {
+      return;
+    }
+
+    let [, widgetNode] = this.getWidgetNode(aWidgetId, window);
+    if (!widgetNode) {
+      log.error("Widget '" + aWidgetId + "' not found, unable to move");
+      return;
+    }
+
+    let areaId = aAreaNode.id;
+    if (isNew) {
+      this.ensureButtonContextMenu(widgetNode, aAreaNode);
+      if (widgetNode.localName == "toolbarbutton" && areaId == CustomizableUI.AREA_PANEL) {
+        widgetNode.setAttribute("wrap", "true");
+      }
+    }
+
+    let [insertionContainer, nextNode] = this.findInsertionPoints(widgetNode, aAreaNode);
+    this.insertWidgetBefore(widgetNode, nextNode, insertionContainer, areaId);
+
+    if (gAreas.get(areaId).get("type") == CustomizableUI.TYPE_TOOLBAR) {
+      aAreaNode.setAttribute("currentset", gPlacements.get(areaId).join(","));
+    }
+  },
+
+  findInsertionPoints(aNode, aAreaNode) {
+    let areaId = aAreaNode.id;
+    let props = gAreas.get(areaId);
+
+    // For overflowable toolbars, rely on them (because the work is more complicated):
+    if (props.get("type") == CustomizableUI.TYPE_TOOLBAR && props.get("overflowable")) {
+      return aAreaNode.overflowable.findOverflowedInsertionPoints(aNode);
+    }
+
+    let container = aAreaNode.customizationTarget;
+    let placements = gPlacements.get(areaId);
+    let nodeIndex = placements.indexOf(aNode.id);
+
+    while (++nodeIndex < placements.length) {
+      let nextNodeId = placements[nodeIndex];
+      let nextNode = container.getElementsByAttribute("id", nextNodeId).item(0);
+
+      if (nextNode) {
+        return [container, nextNode];
+      }
+    }
+
+    return [container, null];
+  },
+
+  insertWidgetBefore(aNode, aNextNode, aContainer, aArea) {
+    this.notifyListeners("onWidgetBeforeDOMChange", aNode, aNextNode, aContainer);
+    this.setLocationAttributes(aNode, aArea);
+    aContainer.insertBefore(aNode, aNextNode);
+    this.notifyListeners("onWidgetAfterDOMChange", aNode, aNextNode, aContainer);
+  },
+
+  handleEvent(aEvent) {
+    switch (aEvent.type) {
+      case "command":
+        if (!this._originalEventInPanel(aEvent)) {
+          break;
+        }
+        aEvent = aEvent.sourceEvent;
+        // Fall through
+      case "click":
+      case "keypress":
+        this.maybeAutoHidePanel(aEvent);
+        break;
+      case "unload":
+        this.unregisterBuildWindow(aEvent.currentTarget);
+        break;
+    }
+  },
+
+  _originalEventInPanel(aEvent) {
+    let e = aEvent.sourceEvent;
+    if (!e) {
+      return false;
+    }
+    let node = this._getPanelForNode(e.target);
+    if (!node) {
+      return false;
+    }
+    let win = e.view;
+    let panels = gPanelsForWindow.get(win);
+    return !!panels && panels.has(node);
+  },
+
+  isSpecialWidget(aId) {
+    return (aId.startsWith(kSpecialWidgetPfx) ||
+            aId.startsWith("separator") ||
+            aId.startsWith("spring") ||
+            aId.startsWith("spacer"));
+  },
+
+  ensureSpecialWidgetId(aId) {
+    let nodeType = aId.match(/spring|spacer|separator/)[0];
+    // If the ID we were passed isn't a generated one, generate one now:
+    if (nodeType == aId) {
+      // Ids are differentiated through a unique count suffix.
+      return kSpecialWidgetPfx + aId + (++gNewElementCount);
+    }
+    return aId;
+  },
+
+  createSpecialWidget(aId, aDocument) {
+    let nodeName = "toolbar" + aId.match(/spring|spacer|separator/)[0];
+    let node = aDocument.createElementNS(kNSXUL, nodeName);
+    node.id = this.ensureSpecialWidgetId(aId);
+    if (nodeName == "toolbarspring") {
+      node.flex = 1;
+    }
+    return node;
+  },
+
+  /* Find a XUL-provided widget in a window. Don't try to use this
+   * for an API-provided widget or a special widget.
+   */
+  findWidgetInWindow(aId, aWindow) {
+    if (!gBuildWindows.has(aWindow)) {
+      throw new Error("Build window not registered");
+    }
+
+    if (!aId) {
+      log.error("findWidgetInWindow was passed an empty string.");
+      return null;
+    }
+
+    let document = aWindow.document;
+
+    // look for a node with the same id, as the node may be
+    // in a different toolbar.
+    let node = document.getElementById(aId);
+    if (node) {
+      let parent = node.parentNode;
+      while (parent && !(parent.customizationTarget ||
+                         parent == aWindow.gNavToolbox.palette)) {
+        parent = parent.parentNode;
+      }
+
+      if (parent) {
+        let nodeInArea = node.parentNode.localName == "toolbarpaletteitem" ?
+                         node.parentNode : node;
+        // Check if we're in a customization target, or in the palette:
+        if ((parent.customizationTarget == nodeInArea.parentNode &&
+             gBuildWindows.get(aWindow).has(parent.toolbox)) ||
+            aWindow.gNavToolbox.palette == nodeInArea.parentNode) {
+          // Normalize the removable attribute. For backwards compat, if
+          // the widget is not located in a toolbox palette then absence
+          // of the "removable" attribute means it is not removable.
+          if (!node.hasAttribute("removable")) {
+            // If we first see this in customization mode, it may be in the
+            // customization palette instead of the toolbox palette.
+            node.setAttribute("removable", !parent.customizationTarget);
+          }
+          return node;
+        }
+      }
+    }
+
+    let toolboxes = gBuildWindows.get(aWindow);
+    for (let toolbox of toolboxes) {
+      if (toolbox.palette) {
+        // Attempt to locate an element with a matching ID within
+        // the palette.
+        let element = toolbox.palette.getElementsByAttribute("id", aId)[0];
+        if (element) {
+          // Normalize the removable attribute. For backwards compat, this
+          // is optional if the widget is located in the toolbox palette,
+          // and defaults to *true*, unlike if it was located elsewhere.
+          if (!element.hasAttribute("removable")) {
+            element.setAttribute("removable", true);
+          }
+          return element;
+        }
+      }
+    }
+    return null;
+  },
+
+  buildWidget(aDocument, aWidget) {
+    if (aDocument.documentURI != kExpectedWindowURL) {
+      throw new Error("buildWidget was called for a non-browser window!");
+    }
+    if (typeof aWidget == "string") {
+      aWidget = gPalette.get(aWidget);
+    }
+    if (!aWidget) {
+      throw new Error("buildWidget was passed a non-widget to build.");
+    }
+
+    log.debug("Building " + aWidget.id + " of type " + aWidget.type);
+
+    let node;
+    if (aWidget.type == "custom") {
+      if (aWidget.onBuild) {
+        node = aWidget.onBuild(aDocument);
+      }
+      if (!node || !(node instanceof aDocument.defaultView.XULElement))
+        log.error("Custom widget with id " + aWidget.id + " does not return a valid node");
+    } else {
+      if (aWidget.onBeforeCreated) {
+        aWidget.onBeforeCreated(aDocument);
+      }
+      node = aDocument.createElementNS(kNSXUL, "toolbarbutton");
+
+      node.setAttribute("id", aWidget.id);
+      node.setAttribute("widget-id", aWidget.id);
+      node.setAttribute("widget-type", aWidget.type);
+      if (aWidget.disabled) {
+        node.setAttribute("disabled", true);
+      }
+      node.setAttribute("removable", aWidget.removable);
+      node.setAttribute("overflows", aWidget.overflows);
+      if (aWidget.tabSpecific) {
+        node.setAttribute("tabspecific", aWidget.tabSpecific);
+      }
+      node.setAttribute("label", this.getLocalizedProperty(aWidget, "label"));
+      let additionalTooltipArguments = [];
+      if (aWidget.shortcutId) {
+        let keyEl = aDocument.getElementById(aWidget.shortcutId);
+        if (keyEl) {
+          additionalTooltipArguments.push(ShortcutUtils.prettifyShortcut(keyEl));
+        } else {
+          log.error("Key element with id '" + aWidget.shortcutId + "' for widget '" + aWidget.id +
+                    "' not found!");
+        }
+      }
+
+      let tooltip = this.getLocalizedProperty(aWidget, "tooltiptext", additionalTooltipArguments);
+      if (tooltip) {
+        node.setAttribute("tooltiptext", tooltip);
+      }
+      node.setAttribute("class", "toolbarbutton-1 chromeclass-toolbar-additional");
+
+      let commandHandler = this.handleWidgetCommand.bind(this, aWidget, node);
+      node.addEventListener("command", commandHandler);
+      let clickHandler = this.handleWidgetClick.bind(this, aWidget, node);
+      node.addEventListener("click", clickHandler);
+
+      // If the widget has a view, and has view showing / hiding listeners,
+      // hook those up to this widget.
+      if (aWidget.type == "view") {
+        log.debug("Widget " + aWidget.id + " has a view. Auto-registering event handlers.");
+        let viewNode = aDocument.getElementById(aWidget.viewId);
+
+        if (viewNode) {
+          // PanelUI relies on the .PanelUI-subView class to be able to show only
+          // one sub-view at a time.
+          viewNode.classList.add("PanelUI-subView");
+
+          for (let eventName of kSubviewEvents) {
+            let handler = "on" + eventName;
+            if (typeof aWidget[handler] == "function") {
+              viewNode.addEventListener(eventName, aWidget[handler]);
+            }
+          }
+
+          log.debug("Widget " + aWidget.id + " showing and hiding event handlers set.");
+        } else {
+          log.error("Could not find the view node with id: " + aWidget.viewId +
+                    ", for widget: " + aWidget.id + ".");
+        }
+      }
+
+      if (aWidget.onCreated) {
+        aWidget.onCreated(node);
+      }
+    }
+
+    aWidget.instances.set(aDocument, node);
+    return node;
+  },
+
+  getLocalizedProperty(aWidget, aProp, aFormatArgs, aDef) {
+    const kReqStringProps = ["label"];
+
+    if (typeof aWidget == "string") {
+      aWidget = gPalette.get(aWidget);
+    }
+    if (!aWidget) {
+      throw new Error("getLocalizedProperty was passed a non-widget to work with.");
+    }
+    let def, name;
+    // Let widgets pass their own string identifiers or strings, so that
+    // we can use strings which aren't the default (in case string ids change)
+    // and so that non-builtin-widgets can also provide labels, tooltips, etc.
+    if (aWidget[aProp] != null) {
+      name = aWidget[aProp];
+      // By using this as the default, if a widget provides a full string rather
+      // than a string ID for localization, we will fall back to that string
+      // and return that.
+      def = aDef || name;
+    } else {
+      name = aWidget.id + "." + aProp;
+      def = aDef || "";
+    }
+    try {
+      if (Array.isArray(aFormatArgs) && aFormatArgs.length) {
+        return gWidgetsBundle.formatStringFromName(name, aFormatArgs,
+          aFormatArgs.length) || def;
+      }
+      return gWidgetsBundle.GetStringFromName(name) || def;
+    } catch (ex) {
+      // If an empty string was explicitly passed, treat it as an actual
+      // value rather than a missing property.
+      if (!def && (name != "" || kReqStringProps.includes(aProp))) {
+        log.error("Could not localize property '" + name + "'.");
+      }
+    }
+    return def;
+  },
+
+  addShortcut(aShortcutNode, aTargetNode = aShortcutNode) {
+    // Detect if we've already been here before.
+    if (aTargetNode.hasAttribute("shortcut"))
+      return;
+
+    let document = aShortcutNode.ownerDocument;
+    let shortcutId = aShortcutNode.getAttribute("key");
+    let shortcut;
+    if (shortcutId) {
+      shortcut = document.getElementById(shortcutId);
+    } else {
+      let commandId = aShortcutNode.getAttribute("command");
+      if (commandId)
+        shortcut = ShortcutUtils.findShortcut(document.getElementById(commandId));
+    }
+    if (!shortcut) {
+      return;
+    }
+
+    aTargetNode.setAttribute("shortcut", ShortcutUtils.prettifyShortcut(shortcut));
+  },
+
+  handleWidgetCommand(aWidget, aNode, aEvent) {
+    log.debug("handleWidgetCommand");
+
+    if (aWidget.type == "button") {
+      if (aWidget.onCommand) {
+        try {
+          aWidget.onCommand.call(null, aEvent);
+        } catch (e) {
+          log.error(e);
+        }
+      } else {
+        // XXXunf Need to think this through more, and formalize.
+        Services.obs.notifyObservers(aNode,
+                                     "customizedui-widget-command",
+                                     aWidget.id);
+      }
+    } else if (aWidget.type == "view") {
+      let ownerWindow = aNode.ownerGlobal;
+      let area = this.getPlacementOfWidget(aNode.id).area;
+      let anchor = aNode;
+      if (area != CustomizableUI.AREA_PANEL) {
+        let wrapper = this.wrapWidget(aWidget.id).forWindow(ownerWindow);
+        if (wrapper && wrapper.anchor) {
+          this.hidePanelForNode(aNode);
+          anchor = wrapper.anchor;
+        }
+      }
+      ownerWindow.PanelUI.showSubView(aWidget.viewId, anchor, area);
+    }
+  },
+
+  handleWidgetClick(aWidget, aNode, aEvent) {
+    log.debug("handleWidgetClick");
+    if (aWidget.onClick) {
+      try {
+        aWidget.onClick.call(null, aEvent);
+      } catch (e) {
+        Cu.reportError(e);
+      }
+    } else {
+      // XXXunf Need to think this through more, and formalize.
+      Services.obs.notifyObservers(aNode, "customizedui-widget-click", aWidget.id);
+    }
+  },
+
+  _getPanelForNode(aNode) {
+    let panel = aNode;
+    while (panel && panel.localName != "panel")
+      panel = panel.parentNode;
+    return panel;
+  },
+
+  /*
+   * If people put things in the panel which need more than single-click interaction,
+   * we don't want to close it. Right now we check for text inputs and menu buttons.
+   * We also check for being outside of any toolbaritem/toolbarbutton, ie on a blank
+   * part of the menu.
+   */
+  _isOnInteractiveElement(aEvent) {
+    function getMenuPopupForDescendant(aNode) {
+      let lastPopup = null;
+      while (aNode && aNode.parentNode &&
+             aNode.parentNode.localName.startsWith("menu")) {
+        lastPopup = aNode.localName == "menupopup" ? aNode : lastPopup;
+        aNode = aNode.parentNode;
+      }
+      return lastPopup;
+    }
+
+    let target = aEvent.originalTarget;
+    let panel = this._getPanelForNode(aEvent.currentTarget);
+    // This can happen in e.g. customize mode. If there's no panel,
+    // there's clearly nothing for us to close; pretend we're interactive.
+    if (!panel) {
+      return true;
+    }
+    // We keep track of:
+    // whether we're in an input container (text field)
+    let inInput = false;
+    // whether we're in a popup/context menu
+    let inMenu = false;
+    // whether we're in a toolbarbutton/toolbaritem
+    let inItem = false;
+    // whether the current menuitem has a valid closemenu attribute
+    let menuitemCloseMenu = "auto";
+    // whether the toolbarbutton/item has a valid closemenu attribute.
+    let closemenu = "auto";
+
+    // While keeping track of that, we go from the original target back up,
+    // to the panel if we have to. We bail as soon as we find an input,
+    // a toolbarbutton/item, or the panel:
+    while (true && target) {
+      // Skip out of iframes etc:
+      if (target.nodeType == target.DOCUMENT_NODE) {
+        if (!target.defaultView) {
+          // Err, we're done.
+          break;
+        }
+        // Cue some voodoo
+        target = target.defaultView.QueryInterface(Ci.nsIInterfaceRequestor)
+                                   .getInterface(Ci.nsIWebNavigation)
+                                   .QueryInterface(Ci.nsIDocShell)
+                                   .chromeEventHandler;
+        if (!target) {
+          break;
+        }
+      }
+      let tagName = target.localName;
+      inInput = tagName == "input" || tagName == "textbox";
+      inItem = tagName == "toolbaritem" || tagName == "toolbarbutton";
+      let isMenuItem = tagName == "menuitem";
+      inMenu = inMenu || isMenuItem;
+      if (inItem && target.hasAttribute("closemenu")) {
+        let closemenuVal = target.getAttribute("closemenu");
+        closemenu = (closemenuVal == "single" || closemenuVal == "none") ?
+                    closemenuVal : "auto";
+      }
+
+      if (isMenuItem && target.hasAttribute("closemenu")) {
+        let closemenuVal = target.getAttribute("closemenu");
+        menuitemCloseMenu = (closemenuVal == "single" || closemenuVal == "none") ?
+                            closemenuVal : "auto";
+      }
+      // Break out of the loop immediately for disabled items, as we need to
+      // keep the menu open in that case.
+      if (target.getAttribute("disabled") == "true") {
+        return true;
+      }
+
+      // This isn't in the loop condition because we want to break before
+      // changing |target| if any of these conditions are true
+      if (inInput || inItem || target == panel) {
+        break;
+      }
+      // We need specific code for popups: the item on which they were invoked
+      // isn't necessarily in their parentNode chain:
+      if (isMenuItem) {
+        let topmostMenuPopup = getMenuPopupForDescendant(target);
+        target = (topmostMenuPopup && topmostMenuPopup.triggerNode) ||
+                 target.parentNode;
+      } else {
+        target = target.parentNode;
+      }
+    }
+
+    // If the user clicked a menu item...
+    if (inMenu) {
+      // We care if we're in an input also,
+      // or if the user specified closemenu!="auto":
+      if (inInput || menuitemCloseMenu != "auto") {
+        return true;
+      }
+      // Otherwise, we're probably fine to close the panel
+      return false;
+    }
+    // If we're not in a menu, and we *are* in a type="menu" toolbarbutton,
+    // we'll now interact with the menu
+    if (inItem && target.getAttribute("type") == "menu") {
+      return true;
+    }
+    // If we're not in a menu, and we *are* in a type="menu-button" toolbarbutton,
+    // it depends whether we're in the dropmarker or the 'real' button:
+    if (inItem && target.getAttribute("type") == "menu-button") {
+      // 'real' button (which has a single action):
+      if (target.getAttribute("anonid") == "button") {
+        return closemenu != "none";
+      }
+      // otherwise, this is the outer button, and the user will now
+      // interact with the menu:
+      return true;
+    }
+    return inInput || !inItem;
+  },
+
+  hidePanelForNode(aNode) {
+    let panel = this._getPanelForNode(aNode);
+    if (panel) {
+      panel.hidePopup();
+    }
+  },
+
+  maybeAutoHidePanel(aEvent) {
+    if (aEvent.type == "keypress") {
+      if (aEvent.keyCode != aEvent.DOM_VK_RETURN) {
+        return;
+      }
+      // If the user hit enter/return, we don't check preventDefault - it makes sense
+      // that this was prevented, but we probably still want to close the panel.
+      // If consumers don't want this to happen, they should specify the closemenu
+      // attribute.
+
+    } else if (aEvent.type != "command") { // mouse events:
+      if (aEvent.defaultPrevented || aEvent.button != 0) {
+        return;
+      }
+      let isInteractive = this._isOnInteractiveElement(aEvent);
+      log.debug("maybeAutoHidePanel: interactive ? " + isInteractive);
+      if (isInteractive) {
+        return;
+      }
+    }
+
+    // We can't use event.target because we might have passed a panelview
+    // anonymous content boundary as well, and so target points to the
+    // panelmultiview in that case. Unfortunately, this means we get
+    // anonymous child nodes instead of the real ones, so looking for the
+    // 'stoooop, don't close me' attributes is more involved.
+    let target = aEvent.originalTarget;
+    let closemenu = "auto";
+    let widgetType = "button";
+    while (target.parentNode && target.localName != "panel") {
+      closemenu = target.getAttribute("closemenu");
+      widgetType = target.getAttribute("widget-type");
+      if (closemenu == "none" || closemenu == "single" ||
+          widgetType == "view") {
+        break;
+      }
+      target = target.parentNode;
+    }
+    if (closemenu == "none" || widgetType == "view") {
+      return;
+    }
+
+    if (closemenu == "single") {
+      let panel = this._getPanelForNode(target);
+      let multiview = panel.querySelector("panelmultiview");
+      if (multiview.showingSubView) {
+        multiview.showMainView();
+        return;
+      }
+    }
+
+    // If we get here, we can actually hide the popup:
+    this.hidePanelForNode(aEvent.target);
+  },
+
+  getUnusedWidgets(aWindowPalette) {
+    let window = aWindowPalette.ownerGlobal;
+    let isWindowPrivate = PrivateBrowsingUtils.isWindowPrivate(window);
+    // We use a Set because there can be overlap between the widgets in
+    // gPalette and the items in the palette, especially after the first
+    // customization, since programmatically generated widgets will remain
+    // in the toolbox palette.
+    let widgets = new Set();
+
+    // It's possible that some widgets have been defined programmatically and
+    // have not been overlayed into the palette. We can find those inside
+    // gPalette.
+    for (let [id, widget] of gPalette) {
+      if (!widget.currentArea) {
+        if (widget.showInPrivateBrowsing || !isWindowPrivate) {
+          widgets.add(id);
+        }
+      }
+    }
+
+    log.debug("Iterating the actual nodes of the window palette");
+    for (let node of aWindowPalette.children) {
+      log.debug("In palette children: " + node.id);
+      if (node.id && !this.getPlacementOfWidget(node.id)) {
+        widgets.add(node.id);
+      }
+    }
+
+    return [...widgets];
+  },
+
+  getPlacementOfWidget(aWidgetId, aOnlyRegistered, aDeadAreas) {
+    if (aOnlyRegistered && !this.widgetExists(aWidgetId)) {
+      return null;
+    }
+
+    for (let [area, placements] of gPlacements) {
+      if (!gAreas.has(area) && !aDeadAreas) {
+        continue;
+      }
+      let index = placements.indexOf(aWidgetId);
+      if (index != -1) {
+        return { area, position: index };
+      }
+    }
+
+    return null;
+  },
+
+  widgetExists(aWidgetId) {
+    if (gPalette.has(aWidgetId) || this.isSpecialWidget(aWidgetId)) {
+      return true;
+    }
+
+    // Destroyed API widgets are in gSeenWidgets, but not in gPalette:
+    if (gSeenWidgets.has(aWidgetId)) {
+      return false;
+    }
+
+    // We're assuming XUL widgets always exist, as it's much harder to check,
+    // and checking would be much more error prone.
+    return true;
+  },
+
+  addWidgetToArea(aWidgetId, aArea, aPosition, aInitialAdd) {
+    if (!gAreas.has(aArea)) {
+      throw new Error("Unknown customization area: " + aArea);
+    }
+
+    // Hack: don't want special widgets in the panel (need to check here as well
+    // as in canWidgetMoveToArea because the menu panel is lazy):
+    if (gAreas.get(aArea).get("type") == CustomizableUI.TYPE_MENU_PANEL &&
+        this.isSpecialWidget(aWidgetId)) {
+      return;
+    }
+
+    // If this is a lazy area that hasn't been restored yet, we can't yet modify
+    // it - would would at least like to add to it. So we keep track of it in
+    // gFuturePlacements,  and use that to add it when restoring the area. We
+    // throw away aPosition though, as that can only be bogus if the area hasn't
+    // yet been restorted (caller can't possibly know where its putting the
+    // widget in relation to other widgets).
+    if (this.isAreaLazy(aArea)) {
+      gFuturePlacements.get(aArea).add(aWidgetId);
+      return;
+    }
+
+    if (this.isSpecialWidget(aWidgetId)) {
+      aWidgetId = this.ensureSpecialWidgetId(aWidgetId);
+    }
+
+    let oldPlacement = this.getPlacementOfWidget(aWidgetId, false, true);
+    if (oldPlacement && oldPlacement.area == aArea) {
+      this.moveWidgetWithinArea(aWidgetId, aPosition);
+      return;
+    }
+
+    // Do nothing if the widget is not allowed to move to the target area.
+    if (!this.canWidgetMoveToArea(aWidgetId, aArea)) {
+      return;
+    }
+
+    if (oldPlacement) {
+      this.removeWidgetFromArea(aWidgetId);
+    }
+
+    if (!gPlacements.has(aArea)) {
+      gPlacements.set(aArea, [aWidgetId]);
+      aPosition = 0;
+    } else {
+      let placements = gPlacements.get(aArea);
+      if (typeof aPosition != "number") {
+        aPosition = placements.length;
+      }
+      if (aPosition < 0) {
+        aPosition = 0;
+      }
+      placements.splice(aPosition, 0, aWidgetId);
+    }
+
+    let widget = gPalette.get(aWidgetId);
+    if (widget) {
+      widget.currentArea = aArea;
+      widget.currentPosition = aPosition;
+    }
+
+    // We initially set placements with addWidgetToArea, so in that case
+    // we don't consider the area "dirtied".
+    if (!aInitialAdd) {
+      gDirtyAreaCache.add(aArea);
+    }
+
+    gDirty = true;
+    this.saveState();
+
+    this.notifyListeners("onWidgetAdded", aWidgetId, aArea, aPosition);
+  },
+
+  removeWidgetFromArea(aWidgetId) {
+    let oldPlacement = this.getPlacementOfWidget(aWidgetId, false, true);
+    if (!oldPlacement) {
+      return;
+    }
+
+    if (!this.isWidgetRemovable(aWidgetId)) {
+      return;
+    }
+
+    let placements = gPlacements.get(oldPlacement.area);
+    let position = placements.indexOf(aWidgetId);
+    if (position != -1) {
+      placements.splice(position, 1);
+    }
+
+    let widget = gPalette.get(aWidgetId);
+    if (widget) {
+      widget.currentArea = null;
+      widget.currentPosition = null;
+    }
+
+    gDirty = true;
+    this.saveState();
+    gDirtyAreaCache.add(oldPlacement.area);
+
+    this.notifyListeners("onWidgetRemoved", aWidgetId, oldPlacement.area);
+  },
+
+  moveWidgetWithinArea(aWidgetId, aPosition) {
+    let oldPlacement = this.getPlacementOfWidget(aWidgetId);
+    if (!oldPlacement) {
+      return;
+    }
+
+    let placements = gPlacements.get(oldPlacement.area);
+    if (typeof aPosition != "number") {
+      aPosition = placements.length;
+    } else if (aPosition < 0) {
+      aPosition = 0;
+    } else if (aPosition > placements.length) {
+      aPosition = placements.length;
+    }
+
+    let widget = gPalette.get(aWidgetId);
+    if (widget) {
+      widget.currentPosition = aPosition;
+      widget.currentArea = oldPlacement.area;
+    }
+
+    if (aPosition == oldPlacement.position) {
+      return;
+    }
+
+    placements.splice(oldPlacement.position, 1);
+    // If we just removed the item from *before* where it is now added,
+    // we need to compensate the position offset for that:
+    if (oldPlacement.position < aPosition) {
+      aPosition--;
+    }
+    placements.splice(aPosition, 0, aWidgetId);
+
+    gDirty = true;
+    gDirtyAreaCache.add(oldPlacement.area);
+
+    this.saveState();
+
+    this.notifyListeners("onWidgetMoved", aWidgetId, oldPlacement.area,
+                         oldPlacement.position, aPosition);
+  },
+
+  // Note that this does not populate gPlacements, which is done lazily so that
+  // the legacy state can be migrated, which is only available once a browser
+  // window is openned.
+  // The panel area is an exception here, since it has no legacy state and is
+  // built lazily - and therefore wouldn't otherwise result in restoring its
+  // state immediately when a browser window opens, which is important for
+  // other consumers of this API.
+  loadSavedState() {
+    let state = null;
+    try {
+      state = Services.prefs.getCharPref(kPrefCustomizationState);
+    } catch (e) {
+      log.debug("No saved state found");
+      // This will fail if nothing has been customized, so silently fall back to
+      // the defaults.
+    }
+
+    if (!state) {
+      return;
+    }
+    try {
+      gSavedState = JSON.parse(state);
+      if (typeof gSavedState != "object" || gSavedState === null) {
+        throw "Invalid saved state";
+      }
+    } catch (e) {
+      Services.prefs.clearUserPref(kPrefCustomizationState);
+      gSavedState = {};
+      log.debug("Error loading saved UI customization state, falling back to defaults.");
+    }
+
+    if (!("placements" in gSavedState)) {
+      gSavedState.placements = {};
+    }
+
+    if (!("currentVersion" in gSavedState)) {
+      gSavedState.currentVersion = 0;
+    }
+
+    gSeenWidgets = new Set(gSavedState.seen || []);
+    gDirtyAreaCache = new Set(gSavedState.dirtyAreaCache || []);
+    gNewElementCount = gSavedState.newElementCount || 0;
+  },
+
+  restoreStateForArea(aArea, aLegacyState) {
+    let placementsPreexisted = gPlacements.has(aArea);
+
+    this.beginBatchUpdate();
+    try {
+      gRestoring = true;
+
+      let restored = false;
+      if (placementsPreexisted) {
+        log.debug("Restoring " + aArea + " from pre-existing placements");
+        for (let [position, id] of gPlacements.get(aArea).entries()) {
+          this.moveWidgetWithinArea(id, position);
+        }
+        gDirty = false;
+        restored = true;
+      } else {
+        gPlacements.set(aArea, []);
+      }
+
+      if (!restored && gSavedState && aArea in gSavedState.placements) {
+        log.debug("Restoring " + aArea + " from saved state");
+        let placements = gSavedState.placements[aArea];
+        for (let id of placements)
+          this.addWidgetToArea(id, aArea);
+        gDirty = false;
+        restored = true;
+      }
+
+      if (!restored && aLegacyState) {
+        log.debug("Restoring " + aArea + " from legacy state");
+        for (let id of aLegacyState)
+          this.addWidgetToArea(id, aArea);
+        // Don't override dirty state, to ensure legacy state is saved here and
+        // therefore only used once.
+        restored = true;
+      }
+
+      if (!restored) {
+        log.debug("Restoring " + aArea + " from default state");
+        let defaults = gAreas.get(aArea).get("defaultPlacements");
+        if (defaults) {
+          for (let id of defaults)
+            this.addWidgetToArea(id, aArea, null, true);
+        }
+        gDirty = false;
+      }
+
+      // Finally, add widgets to the area that were added before the it was able
+      // to be restored. This can occur when add-ons register widgets for a
+      // lazily-restored area before it's been restored.
+      if (gFuturePlacements.has(aArea)) {
+        for (let id of gFuturePlacements.get(aArea))
+          this.addWidgetToArea(id, aArea);
+        gFuturePlacements.delete(aArea);
+      }
+
+      log.debug("Placements for " + aArea + ":\n\t" + gPlacements.get(aArea).join("\n\t"));
+
+      gRestoring = false;
+    } finally {
+      this.endBatchUpdate();
+    }
+  },
+
+  saveState() {
+    if (gInBatchStack || !gDirty) {
+      return;
+    }
+    // Clone because we want to modify this map:
+    let state = { placements: new Map(gPlacements),
+                  seen: gSeenWidgets,
+                  dirtyAreaCache: gDirtyAreaCache,
+                  currentVersion: kVersion,
+                  newElementCount: gNewElementCount };
+
+    // Merge in previously saved areas if not present in gPlacements.
+    // This way, state is still persisted for e.g. temporarily disabled
+    // add-ons - see bug 989338.
+    if (gSavedState && gSavedState.placements) {
+      for (let area of Object.keys(gSavedState.placements)) {
+        if (!state.placements.has(area)) {
+          let placements = gSavedState.placements[area];
+          state.placements.set(area, placements);
+        }
+      }
+    }
+
+    log.debug("Saving state.");
+    let serialized = JSON.stringify(state, this.serializerHelper);
+    log.debug("State saved as: " + serialized);
+    Services.prefs.setCharPref(kPrefCustomizationState, serialized);
+    gDirty = false;
+  },
+
+  serializerHelper(aKey, aValue) {
+    if (typeof aValue == "object" && aValue.constructor.name == "Map") {
+      let result = {};
+      for (let [mapKey, mapValue] of aValue)
+        result[mapKey] = mapValue;
+      return result;
+    }
+
+    if (typeof aValue == "object" && aValue.constructor.name == "Set") {
+      return [...aValue];
+    }
+
+    return aValue;
+  },
+
+  beginBatchUpdate() {
+    gInBatchStack++;
+  },
+
+  endBatchUpdate(aForceDirty) {
+    gInBatchStack--;
+    if (aForceDirty === true) {
+      gDirty = true;
+    }
+    if (gInBatchStack == 0) {
+      this.saveState();
+    } else if (gInBatchStack < 0) {
+      throw new Error("The batch editing stack should never reach a negative number.");
+    }
+  },
+
+  addListener(aListener) {
+    gListeners.add(aListener);
+  },
+
+  removeListener(aListener) {
+    if (aListener == this) {
+      return;
+    }
+
+    gListeners.delete(aListener);
+  },
+
+  notifyListeners(aEvent, ...aArgs) {
+    if (gRestoring) {
+      return;
+    }
+
+    for (let listener of gListeners) {
+      try {
+        if (typeof listener[aEvent] == "function") {
+          listener[aEvent].apply(listener, aArgs);
+        }
+      } catch (e) {
+        log.error(e + " -- " + e.fileName + ":" + e.lineNumber);
+      }
+    }
+  },
+
+  _dispatchToolboxEventToWindow(aEventType, aDetails, aWindow) {
+    let evt = new aWindow.CustomEvent(aEventType, {
+      bubbles: true,
+      cancelable: true,
+      detail: aDetails
+    });
+    aWindow.gNavToolbox.dispatchEvent(evt);
+  },
+
+  dispatchToolboxEvent(aEventType, aDetails = {}, aWindow = null) {
+    if (aWindow) {
+      this._dispatchToolboxEventToWindow(aEventType, aDetails, aWindow);
+      return;
+    }
+    for (let [win, ] of gBuildWindows) {
+      this._dispatchToolboxEventToWindow(aEventType, aDetails, win);
+    }
+  },
+
+  createWidget(aProperties) {
+    let widget = this.normalizeWidget(aProperties, CustomizableUI.SOURCE_EXTERNAL);
+    // XXXunf This should probably throw.
+    if (!widget) {
+      log.error("unable to normalize widget");
+      return undefined;
+    }
+
+    gPalette.set(widget.id, widget);
+
+    // Clear our caches:
+    gGroupWrapperCache.delete(widget.id);
+    for (let [win, ] of gBuildWindows) {
+      let cache = gSingleWrapperCache.get(win);
+      if (cache) {
+        cache.delete(widget.id);
+      }
+    }
+
+    this.notifyListeners("onWidgetCreated", widget.id);
+
+    if (widget.defaultArea) {
+      let addToDefaultPlacements = false;
+      let area = gAreas.get(widget.defaultArea);
+      if (!CustomizableUI.isBuiltinToolbar(widget.defaultArea) &&
+          widget.defaultArea != CustomizableUI.AREA_PANEL) {
+        addToDefaultPlacements = true;
+      }
+
+      if (addToDefaultPlacements) {
+        if (area.has("defaultPlacements")) {
+          area.get("defaultPlacements").push(widget.id);
+        } else {
+          area.set("defaultPlacements", [widget.id]);
+        }
+      }
+    }
+
+    // Look through previously saved state to see if we're restoring a widget.
+    let seenAreas = new Set();
+    let widgetMightNeedAutoAdding = true;
+    for (let [area, ] of gPlacements) {
+      seenAreas.add(area);
+      let areaIsRegistered = gAreas.has(area);
+      let index = gPlacements.get(area).indexOf(widget.id);
+      if (index != -1) {
+        widgetMightNeedAutoAdding = false;
+        if (areaIsRegistered) {
+          widget.currentArea = area;
+          widget.currentPosition = index;
+        }
+        break;
+      }
+    }
+
+    // Also look at saved state data directly in areas that haven't yet been
+    // restored. Can't rely on this for restored areas, as they may have
+    // changed.
+    if (widgetMightNeedAutoAdding && gSavedState) {
+      for (let area of Object.keys(gSavedState.placements)) {
+        if (seenAreas.has(area)) {
+          continue;
+        }
+
+        let areaIsRegistered = gAreas.has(area);
+        let index = gSavedState.placements[area].indexOf(widget.id);
+        if (index != -1) {
+          widgetMightNeedAutoAdding = false;
+          if (areaIsRegistered) {
+            widget.currentArea = area;
+            widget.currentPosition = index;
+          }
+          break;
+        }
+      }
+    }
+
+    // If we're restoring the widget to it's old placement, fire off the
+    // onWidgetAdded event - our own handler will take care of adding it to
+    // any build areas.
+    this.beginBatchUpdate();
+    try {
+      if (widget.currentArea) {
+        this.notifyListeners("onWidgetAdded", widget.id, widget.currentArea,
+                             widget.currentPosition);
+      } else if (widgetMightNeedAutoAdding) {
+        let autoAdd = true;
+        try {
+          autoAdd = Services.prefs.getBoolPref(kPrefCustomizationAutoAdd);
+        } catch (e) {}
+
+        // If the widget doesn't have an existing placement, and it hasn't been
+        // seen before, then add it to its default area so it can be used.
+        // If the widget is not removable, we *have* to add it to its default
+        // area here.
+        let canBeAutoAdded = autoAdd && !gSeenWidgets.has(widget.id);
+        if (!widget.currentArea && (!widget.removable || canBeAutoAdded)) {
+          if (widget.defaultArea) {
+            if (this.isAreaLazy(widget.defaultArea)) {
+              gFuturePlacements.get(widget.defaultArea).add(widget.id);
+            } else {
+              this.addWidgetToArea(widget.id, widget.defaultArea);
+            }
+          }
+        }
+      }
+    } finally {
+      // Ensure we always have this widget in gSeenWidgets, and save
+      // state in case this needs to be done here.
+      gSeenWidgets.add(widget.id);
+      this.endBatchUpdate(true);
+    }
+
+    this.notifyListeners("onWidgetAfterCreation", widget.id, widget.currentArea);
+    return widget.id;
+  },
+
+  createBuiltinWidget(aData) {
+    // This should only ever be called on startup, before any windows are
+    // opened - so we know there's no build areas to handle. Also, builtin
+    // widgets are expected to be (mostly) static, so shouldn't affect the
+    // current placement settings.
+
+    // This allows a widget to be both built-in by default but also able to be
+    // destroyed and removed from the area based on criteria that may not be
+    // available when the widget is created -- for example, because some other
+    // feature in the browser supersedes the widget.
+    let conditionalDestroyPromise = aData.conditionalDestroyPromise || null;
+    delete aData.conditionalDestroyPromise;
+
+    let widget = this.normalizeWidget(aData, CustomizableUI.SOURCE_BUILTIN);
+    if (!widget) {
+      log.error("Error creating builtin widget: " + aData.id);
+      return;
+    }
+
+    log.debug("Creating built-in widget with id: " + widget.id);
+    gPalette.set(widget.id, widget);
+
+    if (conditionalDestroyPromise) {
+      conditionalDestroyPromise.then(shouldDestroy => {
+        if (shouldDestroy) {
+          this.destroyWidget(widget.id);
+          this.removeWidgetFromArea(widget.id);
+        }
+      }, err => {
+        Cu.reportError(err);
+      });
+    }
+  },
+
+  // Returns true if the area will eventually lazily restore (but hasn't yet).
+  isAreaLazy(aArea) {
+    if (gPlacements.has(aArea)) {
+      return false;
+    }
+    return gAreas.get(aArea).has("legacy");
+  },
+
+  // XXXunf Log some warnings here, when the data provided isn't up to scratch.
+  normalizeWidget(aData, aSource) {
+    let widget = {
+      implementation: aData,
+      source: aSource || CustomizableUI.SOURCE_EXTERNAL,
+      instances: new Map(),
+      currentArea: null,
+      removable: true,
+      overflows: true,
+      defaultArea: null,
+      shortcutId: null,
+      tabSpecific: false,
+      tooltiptext: null,
+      showInPrivateBrowsing: true,
+      _introducedInVersion: -1,
+    };
+
+    if (typeof aData.id != "string" || !/^[a-z0-9-_]{1,}$/i.test(aData.id)) {
+      log.error("Given an illegal id in normalizeWidget: " + aData.id);
+      return null;
+    }
+
+    delete widget.implementation.currentArea;
+    widget.implementation.__defineGetter__("currentArea", () => widget.currentArea);
+
+    const kReqStringProps = ["id"];
+    for (let prop of kReqStringProps) {
+      if (typeof aData[prop] != "string") {
+        log.error("Missing required property '" + prop + "' in normalizeWidget: "
+                  + aData.id);
+        return null;
+      }
+      widget[prop] = aData[prop];
+    }
+
+    const kOptStringProps = ["label", "tooltiptext", "shortcutId"];
+    for (let prop of kOptStringProps) {
+      if (typeof aData[prop] == "string") {
+        widget[prop] = aData[prop];
+      }
+    }
+
+    const kOptBoolProps = ["removable", "showInPrivateBrowsing", "overflows", "tabSpecific"];
+    for (let prop of kOptBoolProps) {
+      if (typeof aData[prop] == "boolean") {
+        widget[prop] = aData[prop];
+      }
+    }
+
+    // When we normalize builtin widgets, areas have not yet been registered:
+    if (aData.defaultArea &&
+        (aSource == CustomizableUI.SOURCE_BUILTIN || gAreas.has(aData.defaultArea))) {
+      widget.defaultArea = aData.defaultArea;
+    } else if (!widget.removable) {
+      log.error("Widget '" + widget.id + "' is not removable but does not specify " +
+                "a valid defaultArea. That's not possible; it must specify a " +
+                "valid defaultArea as well.");
+      return null;
+    }
+
+    if ("type" in aData && gSupportedWidgetTypes.has(aData.type)) {
+      widget.type = aData.type;
+    } else {
+      widget.type = "button";
+    }
+
+    widget.disabled = aData.disabled === true;
+
+    if (aSource == CustomizableUI.SOURCE_BUILTIN) {
+      widget._introducedInVersion = aData.introducedInVersion || 0;
+    }
+
+    this.wrapWidgetEventHandler("onBeforeCreated", widget);
+    this.wrapWidgetEventHandler("onClick", widget);
+    this.wrapWidgetEventHandler("onCreated", widget);
+    this.wrapWidgetEventHandler("onDestroyed", widget);
+
+    if (widget.type == "button") {
+      widget.onCommand = typeof aData.onCommand == "function" ?
+                           aData.onCommand :
+                           null;
+    } else if (widget.type == "view") {
+      if (typeof aData.viewId != "string") {
+        log.error("Expected a string for widget " + widget.id + " viewId, but got "
+                  + aData.viewId);
+        return null;
+      }
+      widget.viewId = aData.viewId;
+
+      this.wrapWidgetEventHandler("onViewShowing", widget);
+      this.wrapWidgetEventHandler("onViewHiding", widget);
+    } else if (widget.type == "custom") {
+      this.wrapWidgetEventHandler("onBuild", widget);
+    }
+
+    if (gPalette.has(widget.id)) {
+      return null;
+    }
+
+    return widget;
+  },
+
+  wrapWidgetEventHandler(aEventName, aWidget) {
+    if (typeof aWidget.implementation[aEventName] != "function") {
+      aWidget[aEventName] = null;
+      return;
+    }
+    aWidget[aEventName] = function(...aArgs) {
+      // Wrap inside a try...catch to properly log errors, until bug 862627 is
+      // fixed, which in turn might help bug 503244.
+      try {
+        // Don't copy the function to the normalized widget object, instead
+        // keep it on the original object provided to the API so that
+        // additional methods can be implemented and used by the event
+        // handlers.
+        return aWidget.implementation[aEventName].apply(aWidget.implementation,
+                                                        aArgs);
+      } catch (e) {
+        Cu.reportError(e);
+        return undefined;
+      }
+    };
+  },
+
+  destroyWidget(aWidgetId) {
+    let widget = gPalette.get(aWidgetId);
+    if (!widget) {
+      gGroupWrapperCache.delete(aWidgetId);
+      for (let [window, ] of gBuildWindows) {
+        let windowCache = gSingleWrapperCache.get(window);
+        if (windowCache) {
+          windowCache.delete(aWidgetId);
+        }
+      }
+      return;
+    }
+
+    // Remove it from the default placements of an area if it was added there:
+    if (widget.defaultArea) {
+      let area = gAreas.get(widget.defaultArea);
+      if (area) {
+        let defaultPlacements = area.get("defaultPlacements");
+        // We can assume this is present because if a widget has a defaultArea,
+        // we automatically create a defaultPlacements array for that area.
+        let widgetIndex = defaultPlacements.indexOf(aWidgetId);
+        if (widgetIndex != -1) {
+          defaultPlacements.splice(widgetIndex, 1);
+        }
+      }
+    }
+
+    // This will not remove the widget from gPlacements - we want to keep the
+    // setting so the widget gets put back in it's old position if/when it
+    // returns.
+    for (let [window, ] of gBuildWindows) {
+      let windowCache = gSingleWrapperCache.get(window);
+      if (windowCache) {
+        windowCache.delete(aWidgetId);
+      }
+      let widgetNode = window.document.getElementById(aWidgetId) ||
+                       window.gNavToolbox.palette.getElementsByAttribute("id", aWidgetId)[0];
+      if (widgetNode) {
+        let container = widgetNode.parentNode
+        this.notifyListeners("onWidgetBeforeDOMChange", widgetNode, null,
+                             container, true);
+        widgetNode.remove();
+        this.notifyListeners("onWidgetAfterDOMChange", widgetNode, null,
+                             container, true);
+      }
+      if (widget.type == "view") {
+        let viewNode = window.document.getElementById(widget.viewId);
+        if (viewNode) {
+          for (let eventName of kSubviewEvents) {
+            let handler = "on" + eventName;
+            if (typeof widget[handler] == "function") {
+              viewNode.removeEventListener(eventName, widget[handler]);
+            }
+          }
+        }
+      }
+      if (widgetNode && widget.onDestroyed) {
+        widget.onDestroyed(window.document);
+      }
+    }
+
+    gPalette.delete(aWidgetId);
+    gGroupWrapperCache.delete(aWidgetId);
+
+    this.notifyListeners("onWidgetDestroyed", aWidgetId);
+  },
+
+  getCustomizeTargetForArea(aArea, aWindow) {
+    let buildAreaNodes = gBuildAreas.get(aArea);
+    if (!buildAreaNodes) {
+      return null;
+    }
+
+    for (let node of buildAreaNodes) {
+      if (node.ownerGlobal == aWindow) {
+        return node.customizationTarget ? node.customizationTarget : node;
+      }
+    }
+
+    return null;
+  },
+
+  reset() {
+    gResetting = true;
+    this._resetUIState();
+
+    // Rebuild each registered area (across windows) to reflect the state that
+    // was reset above.
+    this._rebuildRegisteredAreas();
+
+    for (let [widgetId, widget] of gPalette) {
+      if (widget.source == CustomizableUI.SOURCE_EXTERNAL) {
+        gSeenWidgets.add(widgetId);
+      }
+    }
+    if (gSeenWidgets.size) {
+      gDirty = true;
+    }
+
+    gResetting = false;
+  },
+
+  _resetUIState() {
+    try {
+      gUIStateBeforeReset.drawInTitlebar = Services.prefs.getBoolPref(kPrefDrawInTitlebar);
+      gUIStateBeforeReset.uiCustomizationState = Services.prefs.getCharPref(kPrefCustomizationState);
+      gUIStateBeforeReset.currentTheme = LightweightThemeManager.currentTheme;
+    } catch (e) { }
+
+    this._resetExtraToolbars();
+
+    Services.prefs.clearUserPref(kPrefCustomizationState);
+    Services.prefs.clearUserPref(kPrefDrawInTitlebar);
+    LightweightThemeManager.currentTheme = null;
+    log.debug("State reset");
+
+    // Reset placements to make restoring default placements possible.
+    gPlacements = new Map();
+    gDirtyAreaCache = new Set();
+    gSeenWidgets = new Set();
+    // Clear the saved state to ensure that defaults will be used.
+    gSavedState = null;
+    // Restore the state for each area to its defaults
+    for (let [areaId, ] of gAreas) {
+      this.restoreStateForArea(areaId);
+    }
+  },
+
+  _resetExtraToolbars(aFilter = null) {
+    let firstWindow = true; // Only need to unregister and persist once
+    for (let [win, ] of gBuildWindows) {
+      let toolbox = win.gNavToolbox;
+      for (let child of toolbox.children) {
+        let matchesFilter = !aFilter || aFilter == child.id;
+        if (child.hasAttribute("customindex") && matchesFilter) {
+          let toolbarId = "toolbar" + child.getAttribute("customindex");
+          toolbox.toolbarset.removeAttribute(toolbarId);
+          if (firstWindow) {
+            win.document.persist(toolbox.toolbarset.id, toolbarId);
+            // We have to unregister it properly to ensure we don't kill
+            // XUL widgets which might be in here
+            this.unregisterArea(child.id, true);
+          }
+          child.remove();
+        }
+      }
+      firstWindow = false;
+    }
+  },
+
+  _rebuildRegisteredAreas() {
+    for (let [areaId, areaNodes] of gBuildAreas) {
+      let placements = gPlacements.get(areaId);
+      let isFirstChangedToolbar = true;
+      for (let areaNode of areaNodes) {
+        this.buildArea(areaId, placements, areaNode);
+
+        let area = gAreas.get(areaId);
+        if (area.get("type") == CustomizableUI.TYPE_TOOLBAR) {
+          let defaultCollapsed = area.get("defaultCollapsed");
+          let win = areaNode.ownerGlobal;
+          if (defaultCollapsed !== null) {
+            win.setToolbarVisibility(areaNode, !defaultCollapsed, isFirstChangedToolbar);
+          }
+        }
+        isFirstChangedToolbar = false;
+      }
+    }
+  },
+
+  /**
+   * Undoes a previous reset, restoring the state of the UI to the state prior to the reset.
+   */
+  undoReset() {
+    if (gUIStateBeforeReset.uiCustomizationState == null ||
+        gUIStateBeforeReset.drawInTitlebar == null) {
+      return;
+    }
+    gUndoResetting = true;
+
+    let uiCustomizationState = gUIStateBeforeReset.uiCustomizationState;
+    let drawInTitlebar = gUIStateBeforeReset.drawInTitlebar;
+    let currentTheme = gUIStateBeforeReset.currentTheme;
+
+    // Need to clear the previous state before setting the prefs
+    // because pref observers may check if there is a previous UI state.
+    this._clearPreviousUIState();
+
+    Services.prefs.setCharPref(kPrefCustomizationState, uiCustomizationState);
+    Services.prefs.setBoolPref(kPrefDrawInTitlebar, drawInTitlebar);
+    LightweightThemeManager.currentTheme = currentTheme;
+    this.loadSavedState();
+    // If the user just customizes toolbar/titlebar visibility, gSavedState will be null
+    // and we don't need to do anything else here:
+    if (gSavedState) {
+      for (let areaId of Object.keys(gSavedState.placements)) {
+        let placements = gSavedState.placements[areaId];
+        gPlacements.set(areaId, placements);
+      }
+      this._rebuildRegisteredAreas();
+    }
+
+    gUndoResetting = false;
+  },
+
+  _clearPreviousUIState() {
+    Object.getOwnPropertyNames(gUIStateBeforeReset).forEach((prop) => {
+      gUIStateBeforeReset[prop] = null;
+    });
+  },
+
+  removeExtraToolbar(aToolbarId) {
+    this._resetExtraToolbars(aToolbarId);
+  },
+
+  /**
+   * @param {String|Node} aWidget - widget ID or a widget node (preferred for performance).
+   * @return {Boolean} whether the widget is removable
+   */
+  isWidgetRemovable(aWidget) {
+    let widgetId;
+    let widgetNode;
+    if (typeof aWidget == "string") {
+      widgetId = aWidget;
+    } else {
+      widgetId = aWidget.id;
+      widgetNode = aWidget;
+    }
+    let provider = this.getWidgetProvider(widgetId);
+
+    if (provider == CustomizableUI.PROVIDER_API) {
+      return gPalette.get(widgetId).removable;
+    }
+
+    if (provider == CustomizableUI.PROVIDER_XUL) {
+      if (gBuildWindows.size == 0) {
+        // We don't have any build windows to look at, so just assume for now
+        // that its removable.
+        return true;
+      }
+
+      if (!widgetNode) {
+        // Pick any of the build windows to look at.
+        let [window, ] = [...gBuildWindows][0];
+        [, widgetNode] = this.getWidgetNode(widgetId, window);
+      }
+      // If we don't have a node, we assume it's removable. This can happen because
+      // getWidgetProvider returns PROVIDER_XUL by default, but this will also happen
+      // for API-provided widgets which have been destroyed.
+      if (!widgetNode) {
+        return true;
+      }
+      return widgetNode.getAttribute("removable") == "true";
+    }
+
+    // Otherwise this is either a special widget, which is always removable, or
+    // an API widget which has already been removed from gPalette. Returning true
+    // here allows us to then remove its ID from any placements where it might
+    // still occur.
+    return true;
+  },
+
+  canWidgetMoveToArea(aWidgetId, aArea) {
+    let placement = this.getPlacementOfWidget(aWidgetId);
+    if (placement && placement.area != aArea) {
+      // Special widgets can't move to the menu panel.
+      if (this.isSpecialWidget(aWidgetId) && gAreas.has(aArea) &&
+          gAreas.get(aArea).get("type") == CustomizableUI.TYPE_MENU_PANEL) {
+        return false;
+      }
+      // For everything else, just return whether the widget is removable.
+      return this.isWidgetRemovable(aWidgetId);
+    }
+
+    return true;
+  },
+
+  ensureWidgetPlacedInWindow(aWidgetId, aWindow) {
+    let placement = this.getPlacementOfWidget(aWidgetId);
+    if (!placement) {
+      return false;
+    }
+    let areaNodes = gBuildAreas.get(placement.area);
+    if (!areaNodes) {
+      return false;
+    }
+    let container = [...areaNodes].filter((n) => n.ownerGlobal == aWindow);
+    if (!container.length) {
+      return false;
+    }
+    let existingNode = container[0].getElementsByAttribute("id", aWidgetId)[0];
+    if (existingNode) {
+      return true;
+    }
+
+    this.insertNodeInWindow(aWidgetId, container[0], true);
+    return true;
+  },
+
+  get inDefaultState() {
+    for (let [areaId, props] of gAreas) {
+      let defaultPlacements = props.get("defaultPlacements");
+      // Areas without default placements (like legacy ones?) get skipped
+      if (!defaultPlacements) {
+        continue;
+      }
+
+      let currentPlacements = gPlacements.get(areaId);
+      // We're excluding all of the placement IDs for items that do not exist,
+      // and items that have removable="false",
+      // because we don't want to consider them when determining if we're
+      // in the default state. This way, if an add-on introduces a widget
+      // and is then uninstalled, the leftover placement doesn't cause us to
+      // automatically assume that the buttons are not in the default state.
+      let buildAreaNodes = gBuildAreas.get(areaId);
+      if (buildAreaNodes && buildAreaNodes.size) {
+        let container = [...buildAreaNodes][0];
+        let removableOrDefault = (itemNodeOrItem) => {
+          let item = (itemNodeOrItem && itemNodeOrItem.id) || itemNodeOrItem;
+          let isRemovable = this.isWidgetRemovable(itemNodeOrItem);
+          let isInDefault = defaultPlacements.indexOf(item) != -1;
+          return isRemovable || isInDefault;
+        };
+        // Toolbars have a currentSet property which also deals correctly with overflown
+        // widgets (if any) - use that instead:
+        if (props.get("type") == CustomizableUI.TYPE_TOOLBAR) {
+          let currentSet = container.currentSet;
+          currentPlacements = currentSet ? currentSet.split(",") : [];
+          currentPlacements = currentPlacements.filter(removableOrDefault);
+        } else {
+          // Clone the array so we don't modify the actual placements...
+          currentPlacements = [...currentPlacements];
+          currentPlacements = currentPlacements.filter((item) => {
+            let itemNode = container.getElementsByAttribute("id", item)[0];
+            return itemNode && removableOrDefault(itemNode || item);
+          });
+        }
+
+        if (props.get("type") == CustomizableUI.TYPE_TOOLBAR) {
+          let attribute = container.getAttribute("type") == "menubar" ? "autohide" : "collapsed";
+          let collapsed = container.getAttribute(attribute) == "true";
+          let defaultCollapsed = props.get("defaultCollapsed");
+          if (defaultCollapsed !== null && collapsed != defaultCollapsed) {
+            log.debug("Found " + areaId + " had non-default toolbar visibility (expected " + defaultCollapsed + ", was " + collapsed + ")");
+            return false;
+          }
+        }
+      }
+      log.debug("Checking default state for " + areaId + ":\n" + currentPlacements.join(",") +
+                "\nvs.\n" + defaultPlacements.join(","));
+
+      if (currentPlacements.length != defaultPlacements.length) {
+        return false;
+      }
+
+      for (let i = 0; i < currentPlacements.length; ++i) {
+        if (currentPlacements[i] != defaultPlacements[i]) {
+          log.debug("Found " + currentPlacements[i] + " in " + areaId + " where " +
+                    defaultPlacements[i] + " was expected!");
+          return false;
+        }
+      }
+    }
+
+    if (Services.prefs.prefHasUserValue(kPrefDrawInTitlebar)) {
+      log.debug(kPrefDrawInTitlebar + " pref is non-default");
+      return false;
+    }
+
+    if (LightweightThemeManager.currentTheme) {
+      log.debug(LightweightThemeManager.currentTheme + " theme is non-default");
+      return false;
+    }
+
+    return true;
+  },
+
+  setToolbarVisibility(aToolbarId, aIsVisible) {
+    // We only persist the attribute the first time.
+    let isFirstChangedToolbar = true;
+    for (let window of CustomizableUI.windows) {
+      let toolbar = window.document.getElementById(aToolbarId);
+      if (toolbar) {
+        window.setToolbarVisibility(toolbar, aIsVisible, isFirstChangedToolbar);
+        isFirstChangedToolbar = false;
+      }
+    }
+  },
+};
+Object.freeze(CustomizableUIInternal);
+
+this.CustomizableUI = {
+  /**
+   * Constant reference to the ID of the menu panel.
+   */
+  AREA_PANEL: "PanelUI-contents",
+  /**
+   * Constant reference to the ID of the navigation toolbar.
+   */
+  AREA_NAVBAR: "nav-bar",
+  /**
+   * Constant reference to the ID of the menubar's toolbar.
+   */
+  AREA_MENUBAR: "toolbar-menubar",
+  /**
+   * Constant reference to the ID of the tabstrip toolbar.
+   */
+  AREA_TABSTRIP: "TabsToolbar",
+  /**
+   * Constant reference to the ID of the bookmarks toolbar.
+   */
+  AREA_BOOKMARKS: "PersonalToolbar",
+  /**
+   * Constant reference to the ID of the addon-bar toolbar shim.
+   * Do not use, this will be removed as soon as reasonably possible.
+   * @deprecated
+   */
+  AREA_ADDONBAR: "addon-bar",
+  /**
+   * Constant indicating the area is a menu panel.
+   */
+  TYPE_MENU_PANEL: "menu-panel",
+  /**
+   * Constant indicating the area is a toolbar.
+   */
+  TYPE_TOOLBAR: "toolbar",
+
+  /**
+   * Constant indicating a XUL-type provider.
+   */
+  PROVIDER_XUL: "xul",
+  /**
+   * Constant indicating an API-type provider.
+   */
+  PROVIDER_API: "api",
+  /**
+   * Constant indicating dynamic (special) widgets: spring, spacer, and separator.
+   */
+  PROVIDER_SPECIAL: "special",
+
+  /**
+   * Constant indicating the widget is built-in
+   */
+  SOURCE_BUILTIN: "builtin",
+  /**
+   * Constant indicating the widget is externally provided
+   * (e.g. by add-ons or other items not part of the builtin widget set).
+   */
+  SOURCE_EXTERNAL: "external",
+
+  /**
+   * The class used to distinguish items that span the entire menu panel.
+   */
+  WIDE_PANEL_CLASS: "panel-wide-item",
+  /**
+   * The (constant) number of columns in the menu panel.
+   */
+  PANEL_COLUMN_COUNT: 3,
+
+  /**
+   * Constant indicating the reason the event was fired was a window closing
+   */
+  REASON_WINDOW_CLOSED: "window-closed",
+  /**
+   * Constant indicating the reason the event was fired was an area being
+   * unregistered separately from window closing mechanics.
+   */
+  REASON_AREA_UNREGISTERED: "area-unregistered",
+
+
+  /**
+   * An iteratable property of windows managed by CustomizableUI.
+   * Note that this can *only* be used as an iterator. ie:
+   *     for (let window of CustomizableUI.windows) { ... }
+   */
+  windows: {
+    *[Symbol.iterator]() {
+      for (let [window, ] of gBuildWindows)
+        yield window;
+    }
+  },
+
+  /**
+   * Add a listener object that will get fired for various events regarding
+   * customization.
+   *
+   * @param aListener the listener object to add
+   *
+   * Not all event handler methods need to be defined.
+   * CustomizableUI will catch exceptions. Events are dispatched
+   * synchronously on the UI thread, so if you can delay any/some of your
+   * processing, that is advisable. The following event handlers are supported:
+   *   - onWidgetAdded(aWidgetId, aArea, aPosition)
+   *     Fired when a widget is added to an area. aWidgetId is the widget that
+   *     was added, aArea the area it was added to, and aPosition the position
+   *     in which it was added.
+   *   - onWidgetMoved(aWidgetId, aArea, aOldPosition, aNewPosition)
+   *     Fired when a widget is moved within its area. aWidgetId is the widget
+   *     that was moved, aArea the area it was moved in, aOldPosition its old
+   *     position, and aNewPosition its new position.
+   *   - onWidgetRemoved(aWidgetId, aArea)
+   *     Fired when a widget is removed from its area. aWidgetId is the widget
+   *     that was removed, aArea the area it was removed from.
+   *
+   *   - onWidgetBeforeDOMChange(aNode, aNextNode, aContainer, aIsRemoval)
+   *     Fired *before* a widget's DOM node is acted upon by CustomizableUI
+   *     (to add, move or remove it). aNode is the DOM node changed, aNextNode
+   *     the DOM node (if any) before which a widget will be inserted,
+   *     aContainer the *actual* DOM container (could be an overflow panel in
+   *     case of an overflowable toolbar), and aWasRemoval is true iff the
+   *     action about to happen is the removal of the DOM node.
+   *   - onWidgetAfterDOMChange(aNode, aNextNode, aContainer, aWasRemoval)
+   *     Like onWidgetBeforeDOMChange, but fired after the change to the DOM
+   *     node of the widget.
+   *
+   *   - onWidgetReset(aNode, aContainer)
+   *     Fired after a reset to default placements moves a widget's node to a
+   *     different location. aNode is the widget's node, aContainer is the
+   *     area it was moved into (NB: it might already have been there and been
+   *     moved to a different position!)
+   *   - onWidgetUndoMove(aNode, aContainer)
+   *     Fired after undoing a reset to default placements moves a widget's
+   *     node to a different location. aNode is the widget's node, aContainer
+   *     is the area it was moved into (NB: it might already have been there
+   *     and been moved to a different position!)
+   *   - onAreaReset(aArea, aContainer)
+   *     Fired after a reset to default placements is complete on an area's
+   *     DOM node. Note that this is fired for each DOM node. aArea is the area
+   *     that was reset, aContainer the DOM node that was reset.
+   *
+   *   - onWidgetCreated(aWidgetId)
+   *     Fired when a widget with id aWidgetId has been created, but before it
+   *     is added to any placements or any DOM nodes have been constructed.
+   *     Only fired for API-based widgets.
+   *   - onWidgetAfterCreation(aWidgetId, aArea)
+   *     Fired after a widget with id aWidgetId has been created, and has been
+   *     added to either its default area or the area in which it was placed
+   *     previously. If the widget has no default area and/or it has never
+   *     been placed anywhere, aArea may be null. Only fired for API-based
+   *     widgets.
+   *   - onWidgetDestroyed(aWidgetId)
+   *     Fired when widgets are destroyed. aWidgetId is the widget that is
+   *     being destroyed. Only fired for API-based widgets.
+   *   - onWidgetInstanceRemoved(aWidgetId, aDocument)
+   *     Fired when a window is unloaded and a widget's instance is destroyed
+   *     because of this. Only fired for API-based widgets.
+   *
+   *   - onWidgetDrag(aWidgetId, aArea)
+   *     Fired both when and after customize mode drag handling system tries
+   *     to determine the width and height of widget aWidgetId when dragged to a
+   *     different area. aArea will be the area the item is dragged to, or
+   *     undefined after the measurements have been done and the node has been
+   *     moved back to its 'regular' area.
+   *
+   *   - onCustomizeStart(aWindow)
+   *     Fired when opening customize mode in aWindow.
+   *   - onCustomizeEnd(aWindow)
+   *     Fired when exiting customize mode in aWindow.
+   *
+   *   - onWidgetOverflow(aNode, aContainer)
+   *     Fired when a widget's DOM node is overflowing its container, a toolbar,
+   *     and will be displayed in the overflow panel.
+   *   - onWidgetUnderflow(aNode, aContainer)
+   *     Fired when a widget's DOM node is *not* overflowing its container, a
+   *     toolbar, anymore.
+   *   - onWindowOpened(aWindow)
+   *     Fired when a window has been opened that is managed by CustomizableUI,
+   *     once all of the prerequisite setup has been done.
+   *   - onWindowClosed(aWindow)
+   *     Fired when a window that has been managed by CustomizableUI has been
+   *     closed.
+   *   - onAreaNodeRegistered(aArea, aContainer)
+   *     Fired after an area node is first built when it is registered. This
+   *     is often when the window has opened, but in the case of add-ons,
+   *     could fire when the node has just been registered with CustomizableUI
+   *     after an add-on update or disable/enable sequence.
+   *   - onAreaNodeUnregistered(aArea, aContainer, aReason)
+   *     Fired when an area node is explicitly unregistered by an API caller,
+   *     or by a window closing. The aReason parameter indicates which of
+   *     these is the case.
+   */
+  addListener(aListener) {
+    CustomizableUIInternal.addListener(aListener);
+  },
+  /**
+   * Remove a listener added with addListener
+   * @param aListener the listener object to remove
+   */
+  removeListener(aListener) {
+    CustomizableUIInternal.removeListener(aListener);
+  },
+
+  /**
+   * Register a customizable area with CustomizableUI.
+   * @param aName   the name of the area to register. Can only contain
+   *                alphanumeric characters, dashes (-) and underscores (_).
+   * @param aProps  the properties of the area. The following properties are
+   *                recognized:
+   *                - type:   the type of area. Either TYPE_TOOLBAR (default) or
+   *                          TYPE_MENU_PANEL;
+   *                - anchor: for a menu panel or overflowable toolbar, the
+   *                          anchoring node for the panel.
+   *                - legacy: set to true if you want customizableui to
+   *                          automatically migrate the currentset attribute
+   *                - overflowable: set to true if your toolbar is overflowable.
+   *                                This requires an anchor, and only has an
+   *                                effect for toolbars.
+   *                - defaultPlacements: an array of widget IDs making up the
+   *                                     default contents of the area
+   *                - defaultCollapsed: (INTERNAL ONLY) applies if the type is TYPE_TOOLBAR, specifies
+   *                                    if toolbar is collapsed by default (default to true).
+   *                                    Specify null to ensure that reset/inDefaultArea don't care
+   *                                    about a toolbar's collapsed state
+   */
+  registerArea(aName, aProperties) {
+    CustomizableUIInternal.registerArea(aName, aProperties);
+  },
+  /**
+   * Register a concrete node for a registered area. This method is automatically
+   * called from any toolbar in the main browser window that has its
+   * "customizable" attribute set to true. There should normally be no need to
+   * call it yourself.
+   *
+   * Note that ideally, you should register your toolbar using registerArea
+   * before any of the toolbars have their XBL bindings constructed (which
+   * will happen when they're added to the DOM and are not hidden). If you
+   * don't, and your toolbar has a defaultset attribute, CustomizableUI will
+   * register it automatically. If your toolbar does not have a defaultset
+   * attribute, the node will be saved for processing when you call
+   * registerArea. Note that CustomizableUI won't restore state in the area,
+   * allow the user to customize it in customize mode, or otherwise deal
+   * with it, until the area has been registered.
+   */
+  registerToolbarNode(aToolbar, aExistingChildren) {
+    CustomizableUIInternal.registerToolbarNode(aToolbar, aExistingChildren);
+  },
+  /**
+   * Register the menu panel node. This method should not be called by anyone
+   * apart from the built-in PanelUI.
+   * @param aPanel the panel DOM node being registered.
+   */
+  registerMenuPanel(aPanel) {
+    CustomizableUIInternal.registerMenuPanel(aPanel);
+  },
+  /**
+   * Unregister a customizable area. The inverse of registerArea.
+   *
+   * Unregistering an area will remove all the (removable) widgets in the
+   * area, which will return to the panel, and destroy all other traces
+   * of the area within CustomizableUI. Note that this means the *contents*
+   * of the area's DOM nodes will be moved to the panel or removed, but
+   * the area's DOM nodes *themselves* will stay.
+   *
+   * Furthermore, by default the placements of the area will be kept in the
+   * saved state (!) and restored if you re-register the area at a later
+   * point. This is useful for e.g. add-ons that get disabled and then
+   * re-enabled (e.g. when they update).
+   *
+   * You can override this last behaviour (and destroy the placements
+   * information in the saved state) by passing true for aDestroyPlacements.
+   *
+   * @param aName              the name of the area to unregister
+   * @param aDestroyPlacements whether to destroy the placements information
+   *                           for the area, too.
+   */
+  unregisterArea(aName, aDestroyPlacements) {
+    CustomizableUIInternal.unregisterArea(aName, aDestroyPlacements);
+  },
+  /**
+   * Add a widget to an area.
+   * If the area to which you try to add is not known to CustomizableUI,
+   * this will throw.
+   * If the area to which you try to add has not yet been restored from its
+   * legacy state, this will postpone the addition.
+   * If the area to which you try to add is the same as the area in which
+   * the widget is currently placed, this will do the same as
+   * moveWidgetWithinArea.
+   * If the widget cannot be removed from its original location, this will
+   * no-op.
+   *
+   * This will fire an onWidgetAdded notification,
+   * and an onWidgetBeforeDOMChange and onWidgetAfterDOMChange notification
+   * for each window CustomizableUI knows about.
+   *
+   * @param aWidgetId the ID of the widget to add
+   * @param aArea     the ID of the area to add the widget to
+   * @param aPosition the position at which to add the widget. If you do not
+   *                  pass a position, the widget will be added to the end
+   *                  of the area.
+   */
+  addWidgetToArea(aWidgetId, aArea, aPosition) {
+    CustomizableUIInternal.addWidgetToArea(aWidgetId, aArea, aPosition);
+  },
+  /**
+   * Remove a widget from its area. If the widget cannot be removed from its
+   * area, or is not in any area, this will no-op. Otherwise, this will fire an
+   * onWidgetRemoved notification, and an onWidgetBeforeDOMChange and
+   * onWidgetAfterDOMChange notification for each window CustomizableUI knows
+   * about.
+   *
+   * @param aWidgetId the ID of the widget to remove
+   */
+  removeWidgetFromArea(aWidgetId) {
+    CustomizableUIInternal.removeWidgetFromArea(aWidgetId);
+  },
+  /**
+   * Move a widget within an area.
+   * If the widget is not in any area, this will no-op.
+   * If the widget is already at the indicated position, this will no-op.
+   *
+   * Otherwise, this will move the widget and fire an onWidgetMoved notification,
+   * and an onWidgetBeforeDOMChange and onWidgetAfterDOMChange notification for
+   * each window CustomizableUI knows about.
+   *
+   * @param aWidgetId the ID of the widget to move
+   * @param aPosition the position to move the widget to.
+   *                  Negative values or values greater than the number of
+   *                  widgets will be interpreted to mean moving the widget to
+   *                  respectively the first or last position.
+   */
+  moveWidgetWithinArea(aWidgetId, aPosition) {
+    CustomizableUIInternal.moveWidgetWithinArea(aWidgetId, aPosition);
+  },
+  /**
+   * Ensure a XUL-based widget created in a window after areas were
+   * initialized moves to its correct position.
+   * This is roughly equivalent to manually looking up the position and using
+   * insertItem in the old API, but a lot less work for consumers.
+   * Always prefer this over using toolbar.insertItem (which might no-op
+   * because it delegates to addWidgetToArea) or, worse, moving items in the
+   * DOM yourself.
+   *
+   * @param aWidgetId the ID of the widget that was just created
+   * @param aWindow the window in which you want to ensure it was added.
+   *
+   * NB: why is this API per-window, you wonder? Because if you need this,
+   * presumably you yourself need to create the widget in all the windows
+   * and need to loop through them anyway.
+   */
+  ensureWidgetPlacedInWindow(aWidgetId, aWindow) {
+    return CustomizableUIInternal.ensureWidgetPlacedInWindow(aWidgetId, aWindow);
+  },
+  /**
+   * Start a batch update of items.
+   * During a batch update, the customization state is not saved to the user's
+   * preferences file, in order to reduce (possibly sync) IO.
+   * Calls to begin/endBatchUpdate may be nested.
+   *
+   * Callers should ensure that NO MATTER WHAT they call endBatchUpdate once
+   * for each call to beginBatchUpdate, even if there are exceptions in the
+   * code in the batch update. Otherwise, for the duration of the
+   * Firefox session, customization state is never saved. Typically, you
+   * would do this using a try...finally block.
+   */
+  beginBatchUpdate() {
+    CustomizableUIInternal.beginBatchUpdate();
+  },
+  /**
+   * End a batch update. See the documentation for beginBatchUpdate above.
+   *
+   * State is not saved if we believe it is identical to the last known
+   * saved state. State is only ever saved when all batch updates have
+   * finished (ie there has been 1 endBatchUpdate call for each
+   * beginBatchUpdate call). If any of the endBatchUpdate calls pass
+   * aForceDirty=true, we will flush to the prefs file.
+   *
+   * @param aForceDirty force CustomizableUI to flush to the prefs file when
+   *                    all batch updates have finished.
+   */
+  endBatchUpdate(aForceDirty) {
+    CustomizableUIInternal.endBatchUpdate(aForceDirty);
+  },
+  /**
+   * Create a widget.
+   *
+   * To create a widget, you should pass an object with its desired
+   * properties. The following properties are supported:
+   *
+   * - id:            the ID of the widget (required).
+   * - type:          a string indicating the type of widget. Possible types
+   *                  are:
+   *                  'button' - for simple button widgets (the default)
+   *                  'view'   - for buttons that open a panel or subview,
+   *                             depending on where they are placed.
+   *                  'custom' - for fine-grained control over the creation
+   *                             of the widget.
+   * - viewId:        Only useful for views (and required there): the id of the
+   *                  <panelview> that should be shown when clicking the widget.
+   * - onBuild(aDoc): Only useful for custom widgets (and required there); a
+   *                  function that will be invoked with the document in which
+   *                  to build a widget. Should return the DOM node that has
+   *                  been constructed.
+   * - onBeforeCreated(aDoc): Attached to all non-custom widgets; a function
+   *                  that will be invoked before the widget gets a DOM node
+   *                  constructed, passing the document in which that will happen.
+   *                  This is useful especially for 'view' type widgets that need
+   *                  to construct their views on the fly (e.g. from bootstrapped
+   *                  add-ons)
+   * - onCreated(aNode): Attached to all widgets; a function that will be invoked
+   *                  whenever the widget has a DOM node constructed, passing the
+   *                  constructed node as an argument.
+   * - onDestroyed(aDoc): Attached to all non-custom widgets; a function that
+   *                  will be invoked after the widget has a DOM node destroyed,
+   *                  passing the document from which it was removed. This is
+   *                  useful especially for 'view' type widgets that need to
+   *                  cleanup after views that were constructed on the fly.
+   * - onCommand(aEvt): Only useful for button widgets; a function that will be
+   *                    invoked when the user activates the button.
+   * - onClick(aEvt): Attached to all widgets; a function that will be invoked
+   *                  when the user clicks the widget.
+   * - onViewShowing(aEvt): Only useful for views; a function that will be
+   *                  invoked when a user shows your view. If any event
+   *                  handler calls aEvt.preventDefault(), the view will
+   *                  not be shown.
+   *
+   *                  The event's `detail` property is an object with an
+   *                  `addBlocker` method. Handlers which need to
+   *                  perform asynchronous operations before the view is
+   *                  shown may pass this method a Promise, which will
+   *                  prevent the view from showing until it resolves.
+   *                  Additionally, if the promise resolves to the exact
+   *                  value `false`, the view will not be shown.
+   * - onViewHiding(aEvt): Only useful for views; a function that will be
+   *                  invoked when a user hides your view.
+   * - tooltiptext:   string to use for the tooltip of the widget
+   * - label:         string to use for the label of the widget
+   * - removable:     whether the widget is removable (optional, default: true)
+   *                  NB: if you specify false here, you must provide a
+   *                  defaultArea, too.
+   * - overflows:     whether widget can overflow when in an overflowable
+   *                  toolbar (optional, default: true)
+   * - defaultArea:   default area to add the widget to
+   *                  (optional, default: none; required if non-removable)
+   * - shortcutId:    id of an element that has a shortcut for this widget
+   *                  (optional, default: null). This is only used to display
+   *                  the shortcut as part of the tooltip for builtin widgets
+   *                  (which have strings inside
+   *                  customizableWidgets.properties). If you're in an add-on,
+   *                  you should not set this property.
+   * - showInPrivateBrowsing: whether to show the widget in private browsing
+   *                          mode (optional, default: true)
+   *
+   * @param aProperties the specifications for the widget.
+   * @return a wrapper around the created widget (see getWidget)
+   */
+  createWidget(aProperties) {
+    return CustomizableUIInternal.wrapWidget(
+      CustomizableUIInternal.createWidget(aProperties)
+    );
+  },
+  /**
+   * Destroy a widget
+   *
+   * If the widget is part of the default placements in an area, this will
+   * remove it from there. It will also remove any DOM instances. However,
+   * it will keep the widget in the placements for whatever area it was
+   * in at the time. You can remove it from there yourself by calling
+   * CustomizableUI.removeWidgetFromArea(aWidgetId).
+   *
+   * @param aWidgetId the ID of the widget to destroy
+   */
+  destroyWidget(aWidgetId) {
+    CustomizableUIInternal.destroyWidget(aWidgetId);
+  },
+  /**
+   * Get a wrapper object with information about the widget.
+   * The object provides the following properties
+   * (all read-only unless otherwise indicated):
+   *
+   * - id:            the widget's ID;
+   * - type:          the type of widget (button, view, custom). For
+   *                  XUL-provided widgets, this is always 'custom';
+   * - provider:      the provider type of the widget, id est one of
+   *                  PROVIDER_API or PROVIDER_XUL;
+   * - forWindow(w):  a method to obtain a single window wrapper for a widget,
+   *                  in the window w passed as the only argument;
+   * - instances:     an array of all instances (single window wrappers)
+   *                  of the widget. This array is NOT live;
+   * - areaType:      the type of the widget's current area
+   * - isGroup:       true; will be false for wrappers around single widget nodes;
+   * - source:        for API-provided widgets, whether they are built-in to
+   *                  Firefox or add-on-provided;
+   * - disabled:      for API-provided widgets, whether the widget is currently
+   *                  disabled. NB: this property is writable, and will toggle
+   *                  all the widgets' nodes' disabled states;
+   * - label:         for API-provied widgets, the label of the widget;
+   * - tooltiptext:   for API-provided widgets, the tooltip of the widget;
+   * - showInPrivateBrowsing: for API-provided widgets, whether the widget is
+   *                          visible in private browsing;
+   *
+   * Single window wrappers obtained through forWindow(someWindow) or from the
+   * instances array have the following properties
+   * (all read-only unless otherwise indicated):
+   *
+   * - id:            the widget's ID;
+   * - type:          the type of widget (button, view, custom). For
+   *                  XUL-provided widgets, this is always 'custom';
+   * - provider:      the provider type of the widget, id est one of
+   *                  PROVIDER_API or PROVIDER_XUL;
+   * - node:          reference to the corresponding DOM node;
+   * - anchor:        the anchor on which to anchor panels opened from this
+   *                  node. This will point to the overflow chevron on
+   *                  overflowable toolbars if and only if your widget node
+   *                  is overflowed, to the anchor for the panel menu
+   *                  if your widget is inside the panel menu, and to the
+   *                  node itself in all other cases;
+   * - overflowed:    boolean indicating whether the node is currently in the
+   *                  overflow panel of the toolbar;
+   * - isGroup:       false; will be true for the group widget;
+   * - label:         for API-provided widgets, convenience getter for the
+   *                  label attribute of the DOM node;
+   * - tooltiptext:   for API-provided widgets, convenience getter for the
+   *                  tooltiptext attribute of the DOM node;
+   * - disabled:      for API-provided widgets, convenience getter *and setter*
+   *                  for the disabled state of this single widget. Note that
+   *                  you may prefer to use the group wrapper's getter/setter
+   *                  instead.
+   *
+   * @param aWidgetId the ID of the widget whose information you need
+   * @return a wrapper around the widget as described above, or null if the
+   *         widget is known not to exist (anymore). NB: non-null return
+   *         is no guarantee the widget exists because we cannot know in
+   *         advance if a XUL widget exists or not.
+   */
+  getWidget(aWidgetId) {
+    return CustomizableUIInternal.wrapWidget(aWidgetId);
+  },
+  /**
+   * Get an array of widget wrappers (see getWidget) for all the widgets
+   * which are currently not in any area (so which are in the palette).
+   *
+   * @param aWindowPalette the palette (and by extension, the window) in which
+   *                       CustomizableUI should look. This matters because of
+   *                       course XUL-provided widgets could be available in
+   *                       some windows but not others, and likewise
+   *                       API-provided widgets might not exist in a private
+   *                       window (because of the showInPrivateBrowsing
+   *                       property).
+   *
+   * @return an array of widget wrappers (see getWidget)
+   */
+  getUnusedWidgets(aWindowPalette) {
+    return CustomizableUIInternal.getUnusedWidgets(aWindowPalette).map(
+      CustomizableUIInternal.wrapWidget,
+      CustomizableUIInternal
+    );
+  },
+  /**
+   * Get an array of all the widget IDs placed in an area. This is roughly
+   * equivalent to fetching the currentset attribute and splitting by commas
+   * in the legacy APIs. Modifying the array will not affect CustomizableUI.
+   *
+   * @param aArea the ID of the area whose placements you want to obtain.
+   * @return an array containing the widget IDs that are in the area.
+   *
+   * NB: will throw if called too early (before placements have been fetched)
+   *     or if the area is not currently known to CustomizableUI.
+   */
+  getWidgetIdsInArea(aArea) {
+    if (!gAreas.has(aArea)) {
+      throw new Error("Unknown customization area: " + aArea);
+    }
+    if (!gPlacements.has(aArea)) {
+      throw new Error("Area not yet restored");
+    }
+
+    // We need to clone this, as we don't want to let consumers muck with placements
+    return [...gPlacements.get(aArea)];
+  },
+  /**
+   * Get an array of widget wrappers for all the widgets in an area. This is
+   * the same as calling getWidgetIdsInArea and .map() ing the result through
+   * CustomizableUI.getWidget. Careful: this means that if there are IDs in there
+   * which don't have corresponding DOM nodes (like in the old-style currentset
+   * attribute), there might be nulls in this array, or items for which
+   * wrapper.forWindow(win) will return null.
+   *
+   * @param aArea the ID of the area whose widgets you want to obtain.
+   * @return an array of widget wrappers and/or null values for the widget IDs
+   *         placed in an area.
+   *
+   * NB: will throw if called too early (before placements have been fetched)
+   *     or if the area is not currently known to CustomizableUI.
+   */
+  getWidgetsInArea(aArea) {
+    return this.getWidgetIdsInArea(aArea).map(
+      CustomizableUIInternal.wrapWidget,
+      CustomizableUIInternal
+    );
+  },
+  /**
+   * Obtain an array of all the area IDs known to CustomizableUI.
+   * This array is created for you, so is modifiable without CustomizableUI
+   * being affected.
+   */
+  get areas() {
+    return [...gAreas.keys()];
+  },
+  /**
+   * Check what kind of area (toolbar or menu panel) an area is. This is
+   * useful if you have a widget that needs to behave differently depending
+   * on its location. Note that widget wrappers have a convenience getter
+   * property (areaType) for this purpose.
+   *
+   * @param aArea the ID of the area whose type you want to know
+   * @return TYPE_TOOLBAR or TYPE_MENU_PANEL depending on the area, null if
+   *         the area is unknown.
+   */
+  getAreaType(aArea) {
+    let area = gAreas.get(aArea);
+    return area ? area.get("type") : null;
+  },
+  /**
+   * Check if a toolbar is collapsed by default.
+   *
+   * @param aArea the ID of the area whose default-collapsed state you want to know.
+   * @return `true` or `false` depending on the area, null if the area is unknown,
+   *         or its collapsed state cannot normally be controlled by the user
+   */
+  isToolbarDefaultCollapsed(aArea) {
+    let area = gAreas.get(aArea);
+    return area ? area.get("defaultCollapsed") : null;
+  },
+  /**
+   * Obtain the DOM node that is the customize target for an area in a
+   * specific window.
+   *
+   * Areas can have a customization target that does not correspond to the
+   * node itself. In particular, toolbars that have a customizationtarget
+   * attribute set will have their customization target set to that node.
+   * This means widgets will end up in the customization target, not in the
+   * DOM node with the ID that corresponds to the area ID. This is useful
+   * because it lets you have fixed content in a toolbar (e.g. the panel
+   * menu item in the navbar) and have all the customizable widgets use
+   * the customization target.
+   *
+   * Using this API yourself is discouraged; you should generally not need
+   * to be asking for the DOM container node used for a particular area.
+   * In particular, if you're wanting to check it in relation to a widget's
+   * node, your DOM node might not be a direct child of the customize target
+   * in a window if, for instance, the window is in customization mode, or if
+   * this is an overflowable toolbar and the widget has been overflowed.
+   *
+   * @param aArea   the ID of the area whose customize target you want to have
+   * @param aWindow the window where you want to fetch the DOM node.
+   * @return the customize target DOM node for aArea in aWindow
+   */
+  getCustomizeTargetForArea(aArea, aWindow) {
+    return CustomizableUIInternal.getCustomizeTargetForArea(aArea, aWindow);
+  },
+  /**
+   * Reset the customization state back to its default.
+   *
+   * This is the nuclear option. You should never call this except if the user
+   * explicitly requests it. Firefox does this when the user clicks the
+   * "Restore Defaults" button in customize mode.
+   */
+  reset() {
+    CustomizableUIInternal.reset();
+  },
+
+  /**
+   * Undo the previous reset, can only be called immediately after a reset.
+   * @return a promise that will be resolved when the operation is complete.
+   */
+  undoReset() {
+    CustomizableUIInternal.undoReset();
+  },
+
+  /**
+   * Remove a custom toolbar added in a previous version of Firefox or using
+   * an add-on. NB: only works on the customizable toolbars generated by
+   * the toolbox itself. Intended for use from CustomizeMode, not by
+   * other consumers.
+   * @param aToolbarId the ID of the toolbar to remove
+   */
+  removeExtraToolbar(aToolbarId) {
+    CustomizableUIInternal.removeExtraToolbar(aToolbarId);
+  },
+
+  /**
+   * Can the last Restore Defaults operation be undone.
+   *
+   * @return A boolean stating whether an undo of the
+   *         Restore Defaults can be performed.
+   */
+  get canUndoReset() {
+    return gUIStateBeforeReset.uiCustomizationState != null ||
+           gUIStateBeforeReset.drawInTitlebar != null ||
+           gUIStateBeforeReset.currentTheme != null;
+  },
+
+  /**
+   * Get the placement of a widget. This is by far the best way to obtain
+   * information about what the state of your widget is. The internals of
+   * this call are cheap (no DOM necessary) and you will know where the user
+   * has put your widget.
+   *
+   * @param aWidgetId the ID of the widget whose placement you want to know
+   * @return
+   *   {
+   *     area: "somearea", // The ID of the area where the widget is placed
+   *     position: 42 // the index in the placements array corresponding to
+   *                  // your widget.
+   *   }
+   *
+   *   OR
+   *
+   *   null // if the widget is not placed anywhere (ie in the palette)
+   */
+  getPlacementOfWidget(aWidgetId, aOnlyRegistered = true, aDeadAreas = false) {
+    return CustomizableUIInternal.getPlacementOfWidget(aWidgetId, aOnlyRegistered, aDeadAreas);
+  },
+  /**
+   * Check if a widget can be removed from the area it's in.
+   *
+   * Note that if you're wanting to move the widget somewhere, you should
+   * generally be checking canWidgetMoveToArea, because that will return
+   * true if the widget is already in the area where you want to move it (!).
+   *
+   * NB: oh, also, this method might lie if the widget in question is a
+   *     XUL-provided widget and there are no windows open, because it
+   *     can obviously not check anything in this case. It will return
+   *     true. You will be able to move the widget elsewhere. However,
+   *     once the user reopens a window, the widget will move back to its
+   *     'proper' area automagically.
+   *
+   * @param aWidgetId a widget ID or DOM node to check
+   * @return true if the widget can be removed from its area,
+   *          false otherwise.
+   */
+  isWidgetRemovable(aWidgetId) {
+    return CustomizableUIInternal.isWidgetRemovable(aWidgetId);
+  },
+  /**
+   * Check if a widget can be moved to a particular area. Like
+   * isWidgetRemovable but better, because it'll return true if the widget
+   * is already in the right area.
+   *
+   * @param aWidgetId the widget ID or DOM node you want to move somewhere
+   * @param aArea     the area ID you want to move it to.
+   * @return true if this is possible, false if it is not. The same caveats as
+   *              for isWidgetRemovable apply, however, if no windows are open.
+   */
+  canWidgetMoveToArea(aWidgetId, aArea) {
+    return CustomizableUIInternal.canWidgetMoveToArea(aWidgetId, aArea);
+  },
+  /**
+   * Whether we're in a default state. Note that non-removable non-default
+   * widgets and non-existing widgets are not taken into account in determining
+   * whether we're in the default state.
+   *
+   * NB: this is a property with a getter. The getter is NOT cheap, because
+   * it does smart things with non-removable non-default items, non-existent
+   * items, and so forth. Please don't call unless necessary.
+   */
+  get inDefaultState() {
+    return CustomizableUIInternal.inDefaultState;
+  },
+
+  /**
+   * Set a toolbar's visibility state in all windows.
+   * @param aToolbarId    the toolbar whose visibility should be adjusted
+   * @param aIsVisible    whether the toolbar should be visible
+   */
+  setToolbarVisibility(aToolbarId, aIsVisible) {
+    CustomizableUIInternal.setToolbarVisibility(aToolbarId, aIsVisible);
+  },
+
+  /**
+   * Get a localized property off a (widget?) object.
+   *
+   * NB: this is unlikely to be useful unless you're in Firefox code, because
+   *     this code uses the builtin widget stringbundle, and can't be told
+   *     to use add-on-provided strings. It's mainly here as convenience for
+   *     custom builtin widgets that build their own DOM but use the same
+   *     stringbundle as the other builtin widgets.
+   *
+   * @param aWidget     the object whose property we should use to fetch a
+   *                    localizable string;
+   * @param aProp       the property on the object to use for the fetching;
+   * @param aFormatArgs (optional) any extra arguments to use for a formatted
+   *                    string;
+   * @param aDef        (optional) the default to return if we don't find the
+   *                    string in the stringbundle;
+   *
+   * @return the localized string, or aDef if the string isn't in the bundle.
+   *         If no default is provided,
+   *           if aProp exists on aWidget, we'll return that,
+   *           otherwise we'll return the empty string
+   *
+   */
+  getLocalizedProperty(aWidget, aProp, aFormatArgs, aDef) {
+    return CustomizableUIInternal.getLocalizedProperty(aWidget, aProp,
+      aFormatArgs, aDef);
+  },
+  /**
+   * Utility function to detect, find and set a keyboard shortcut for a menuitem
+   * or (toolbar)button.
+   *
+   * @param aShortcutNode the XUL node where the shortcut will be derived from;
+   * @param aTargetNode   (optional) the XUL node on which the `shortcut`
+   *                      attribute will be set. If NULL, the shortcut will be
+   *                      set on aShortcutNode;
+   */
+  addShortcut(aShortcutNode, aTargetNode) {
+    return CustomizableUIInternal.addShortcut(aShortcutNode, aTargetNode);
+  },
+  /**
+   * Given a node, walk up to the first panel in its ancestor chain, and
+   * close it.
+   *
+   * @param aNode a node whose panel should be closed;
+   */
+  hidePanelForNode(aNode) {
+    CustomizableUIInternal.hidePanelForNode(aNode);
+  },
+  /**
+   * Check if a widget is a "special" widget: a spring, spacer or separator.
+   *
+   * @param aWidgetId the widget ID to check.
+   * @return true if the widget is 'special', false otherwise.
+   */
+  isSpecialWidget(aWidgetId) {
+    return CustomizableUIInternal.isSpecialWidget(aWidgetId);
+  },
+  /**
+   * Add listeners to a panel that will close it. For use from the menu panel
+   * and overflowable toolbar implementations, unlikely to be useful for
+   * consumers.
+   *
+   * @param aPanel the panel to which listeners should be attached.
+   */
+  addPanelCloseListeners(aPanel) {
+    CustomizableUIInternal.addPanelCloseListeners(aPanel);
+  },
+  /**
+   * Remove close listeners that have been added to a panel with
+   * addPanelCloseListeners. For use from the menu panel and overflowable
+   * toolbar implementations, unlikely to be useful for consumers.
+   *
+   * @param aPanel the panel from which listeners should be removed.
+   */
+  removePanelCloseListeners(aPanel) {
+    CustomizableUIInternal.removePanelCloseListeners(aPanel);
+  },
+  /**
+   * Notify listeners a widget is about to be dragged to an area. For use from
+   * Customize Mode only, do not use otherwise.
+   *
+   * @param aWidgetId the ID of the widget that is being dragged to an area.
+   * @param aArea     the ID of the area to which the widget is being dragged.
+   */
+  onWidgetDrag(aWidgetId, aArea) {
+    CustomizableUIInternal.notifyListeners("onWidgetDrag", aWidgetId, aArea);
+  },
+  /**
+   * Notify listeners that a window is entering customize mode. For use from
+   * Customize Mode only, do not use otherwise.
+   * @param aWindow the window entering customize mode
+   */
+  notifyStartCustomizing(aWindow) {
+    CustomizableUIInternal.notifyListeners("onCustomizeStart", aWindow);
+  },
+  /**
+   * Notify listeners that a window is exiting customize mode. For use from
+   * Customize Mode only, do not use otherwise.
+   * @param aWindow the window exiting customize mode
+   */
+  notifyEndCustomizing(aWindow) {
+    CustomizableUIInternal.notifyListeners("onCustomizeEnd", aWindow);
+  },
+
+  /**
+   * Notify toolbox(es) of a particular event. If you don't pass aWindow,
+   * all toolboxes will be notified. For use from Customize Mode only,
+   * do not use otherwise.
+   * @param aEvent the name of the event to send.
+   * @param aDetails optional, the details of the event.
+   * @param aWindow optional, the window in which to send the event.
+   */
+  dispatchToolboxEvent(aEvent, aDetails = {}, aWindow = null) {
+    CustomizableUIInternal.dispatchToolboxEvent(aEvent, aDetails, aWindow);
+  },
+
+  /**
+   * Check whether an area is overflowable.
+   *
+   * @param aAreaId the ID of an area to check for overflowable-ness
+   * @return true if the area is overflowable, false otherwise.
+   */
+  isAreaOverflowable(aAreaId) {
+    let area = gAreas.get(aAreaId);
+    return area ? area.get("type") == this.TYPE_TOOLBAR && area.get("overflowable")
+                : false;
+  },
+  /**
+   * Obtain a string indicating the place of an element. This is intended
+   * for use from customize mode; You should generally use getPlacementOfWidget
+   * instead, which is cheaper because it does not use the DOM.
+   *
+   * @param aElement the DOM node whose place we need to check
+   * @return "toolbar" if the node is in a toolbar, "panel" if it is in the
+   *         menu panel, "palette" if it is in the (visible!) customization
+   *         palette, undefined otherwise.
+   */
+  getPlaceForItem(aElement) {
+    let place;
+    let node = aElement;
+    while (node && !place) {
+      if (node.localName == "toolbar")
+        place = "toolbar";
+      else if (node.id == CustomizableUI.AREA_PANEL)
+        place = "panel";
+      else if (node.id == "customization-palette")
+        place = "palette";
+
+      node = node.parentNode;
+    }
+    return place;
+  },
+
+  /**
+   * Check if a toolbar is builtin or not.
+   * @param aToolbarId the ID of the toolbar you want to check
+   */
+  isBuiltinToolbar(aToolbarId) {
+    return CustomizableUIInternal._builtinToolbars.has(aToolbarId);
+  },
+};
+Object.freeze(this.CustomizableUI);
+Object.freeze(this.CustomizableUI.windows);
+
+/**
+ * All external consumers of widgets are really interacting with these wrappers
+ * which provide a common interface.
+ */
+
+/**
+ * WidgetGroupWrapper is the common interface for interacting with an entire
+ * widget group - AKA, all instances of a widget across a series of windows.
+ * This particular wrapper is only used for widgets created via the provider
+ * API.
+ */
+function WidgetGroupWrapper(aWidget) {
+  this.isGroup = true;
+
+  const kBareProps = ["id", "source", "type", "disabled", "label", "tooltiptext",
+                      "showInPrivateBrowsing", "viewId"];
+  for (let prop of kBareProps) {
+    let propertyName = prop;
+    this.__defineGetter__(propertyName, () => aWidget[propertyName]);
+  }
+
+  this.__defineGetter__("provider", () => CustomizableUI.PROVIDER_API);
+
+  this.__defineSetter__("disabled", function(aValue) {
+    aValue = !!aValue;
+    aWidget.disabled = aValue;
+    for (let [, instance] of aWidget.instances) {
+      instance.disabled = aValue;
+    }
+  });
+
+  this.forWindow = function WidgetGroupWrapper_forWindow(aWindow) {
+    let wrapperMap;
+    if (!gSingleWrapperCache.has(aWindow)) {
+      wrapperMap = new Map();
+      gSingleWrapperCache.set(aWindow, wrapperMap);
+    } else {
+      wrapperMap = gSingleWrapperCache.get(aWindow);
+    }
+    if (wrapperMap.has(aWidget.id)) {
+      return wrapperMap.get(aWidget.id);
+    }
+
+    let instance = aWidget.instances.get(aWindow.document);
+    if (!instance &&
+        (aWidget.showInPrivateBrowsing || !PrivateBrowsingUtils.isWindowPrivate(aWindow))) {
+      instance = CustomizableUIInternal.buildWidget(aWindow.document,
+                                                    aWidget);
+    }
+
+    let wrapper = new WidgetSingleWrapper(aWidget, instance);
+    wrapperMap.set(aWidget.id, wrapper);
+    return wrapper;
+  };
+
+  this.__defineGetter__("instances", function() {
+    // Can't use gBuildWindows here because some areas load lazily:
+    let placement = CustomizableUIInternal.getPlacementOfWidget(aWidget.id);
+    if (!placement) {
+      return [];
+    }
+    let area = placement.area;
+    let buildAreas = gBuildAreas.get(area);
+    if (!buildAreas) {
+      return [];
+    }
+    return Array.from(buildAreas, (node) => this.forWindow(node.ownerGlobal));
+  });
+
+  this.__defineGetter__("areaType", function() {
+    let areaProps = gAreas.get(aWidget.currentArea);
+    return areaProps && areaProps.get("type");
+  });
+
+  Object.freeze(this);
+}
+
+/**
+ * A WidgetSingleWrapper is a wrapper around a single instance of a widget in
+ * a particular window.
+ */
+function WidgetSingleWrapper(aWidget, aNode) {
+  this.isGroup = false;
+
+  this.node = aNode;
+  this.provider = CustomizableUI.PROVIDER_API;
+
+  const kGlobalProps = ["id", "type"];
+  for (let prop of kGlobalProps) {
+    this[prop] = aWidget[prop];
+  }
+
+  const kNodeProps = ["label", "tooltiptext"];
+  for (let prop of kNodeProps) {
+    let propertyName = prop;
+    // Look at the node for these, instead of the widget data, to ensure the
+    // wrapper always reflects this live instance.
+    this.__defineGetter__(propertyName,
+                          () => aNode.getAttribute(propertyName));
+  }
+
+  this.__defineGetter__("disabled", () => aNode.disabled);
+  this.__defineSetter__("disabled", function(aValue) {
+    aNode.disabled = !!aValue;
+  });
+
+  this.__defineGetter__("anchor", function() {
+    let anchorId;
+    // First check for an anchor for the area:
+    let placement = CustomizableUIInternal.getPlacementOfWidget(aWidget.id);
+    if (placement) {
+      anchorId = gAreas.get(placement.area).get("anchor");
+    }
+    if (!anchorId) {
+      anchorId = aNode.getAttribute("cui-anchorid");
+    }
+
+    return anchorId ? aNode.ownerDocument.getElementById(anchorId)
+                    : aNode;
+  });
+
+  this.__defineGetter__("overflowed", function() {
+    return aNode.getAttribute("overflowedItem") == "true";
+  });
+
+  Object.freeze(this);
+}
+
+/**
+ * XULWidgetGroupWrapper is the common interface for interacting with an entire
+ * widget group - AKA, all instances of a widget across a series of windows.
+ * This particular wrapper is only used for widgets created via the old-school
+ * XUL method (overlays, or programmatically injecting toolbaritems, or other
+ * such things).
+ */
+// XXXunf Going to need to hook this up to some events to keep it all live.
+function XULWidgetGroupWrapper(aWidgetId) {
+  this.isGroup = true;
+  this.id = aWidgetId;
+  this.type = "custom";
+  this.provider = CustomizableUI.PROVIDER_XUL;
+
+  this.forWindow = function XULWidgetGroupWrapper_forWindow(aWindow) {
+    let wrapperMap;
+    if (!gSingleWrapperCache.has(aWindow)) {
+      wrapperMap = new Map();
+      gSingleWrapperCache.set(aWindow, wrapperMap);
+    } else {
+      wrapperMap = gSingleWrapperCache.get(aWindow);
+    }
+    if (wrapperMap.has(aWidgetId)) {
+      return wrapperMap.get(aWidgetId);
+    }
+
+    let instance = aWindow.document.getElementById(aWidgetId);
+    if (!instance) {
+      // Toolbar palettes aren't part of the document, so elements in there
+      // won't be found via document.getElementById().
+      instance = aWindow.gNavToolbox.palette.getElementsByAttribute("id", aWidgetId)[0];
+    }
+
+    let wrapper = new XULWidgetSingleWrapper(aWidgetId, instance, aWindow.document);
+    wrapperMap.set(aWidgetId, wrapper);
+    return wrapper;
+  };
+
+  this.__defineGetter__("areaType", function() {
+    let placement = CustomizableUIInternal.getPlacementOfWidget(aWidgetId);
+    if (!placement) {
+      return null;
+    }
+
+    let areaProps = gAreas.get(placement.area);
+    return areaProps && areaProps.get("type");
+  });
+
+  this.__defineGetter__("instances", function() {
+    return Array.from(gBuildWindows, (wins) => this.forWindow(wins[0]));
+  });
+
+  Object.freeze(this);
+}
+
+/**
+ * A XULWidgetSingleWrapper is a wrapper around a single instance of a XUL
+ * widget in a particular window.
+ */
+function XULWidgetSingleWrapper(aWidgetId, aNode, aDocument) {
+  this.isGroup = false;
+
+  this.id = aWidgetId;
+  this.type = "custom";
+  this.provider = CustomizableUI.PROVIDER_XUL;
+
+  let weakDoc = Cu.getWeakReference(aDocument);
+  // If we keep a strong ref, the weak ref will never die, so null it out:
+  aDocument = null;
+
+  this.__defineGetter__("node", function() {
+    // If we've set this to null (further down), we're sure there's nothing to
+    // be gotten here, so bail out early:
+    if (!weakDoc) {
+      return null;
+    }
+    if (aNode) {
+      // Return the last known node if it's still in the DOM...
+      if (aNode.ownerDocument.contains(aNode)) {
+        return aNode;
+      }
+      // ... or the toolbox
+      let toolbox = aNode.ownerGlobal.gNavToolbox;
+      if (toolbox && toolbox.palette && aNode.parentNode == toolbox.palette) {
+        return aNode;
+      }
+      // If it isn't, clear the cached value and fall through to the "slow" case:
+      aNode = null;
+    }
+
+    let doc = weakDoc.get();
+    if (doc) {
+      // Store locally so we can cache the result:
+      aNode = CustomizableUIInternal.findWidgetInWindow(aWidgetId, doc.defaultView);
+      return aNode;
+    }
+    // The weakref to the document is dead, we're done here forever more:
+    weakDoc = null;
+    return null;
+  });
+
+  this.__defineGetter__("anchor", function() {
+    let anchorId;
+    // First check for an anchor for the area:
+    let placement = CustomizableUIInternal.getPlacementOfWidget(aWidgetId);
+    if (placement) {
+      anchorId = gAreas.get(placement.area).get("anchor");
+    }
+
+    let node = this.node;
+    if (!anchorId && node) {
+      anchorId = node.getAttribute("cui-anchorid");
+    }
+
+    return (anchorId && node) ? node.ownerDocument.getElementById(anchorId) : node;
+  });
+
+  this.__defineGetter__("overflowed", function() {
+    let node = this.node;
+    if (!node) {
+      return false;
+    }
+    return node.getAttribute("overflowedItem") == "true";
+  });
+
+  Object.freeze(this);
+}
+
+const LAZY_RESIZE_INTERVAL_MS = 200;
+const OVERFLOW_PANEL_HIDE_DELAY_MS = 500;
+
+function OverflowableToolbar(aToolbarNode) {
+  this._toolbar = aToolbarNode;
+  this._collapsed = new Map();
+  this._enabled = true;
+
+  this._toolbar.setAttribute("overflowable", "true");
+  let doc = this._toolbar.ownerDocument;
+  this._target = this._toolbar.customizationTarget;
+  this._list = doc.getElementById(this._toolbar.getAttribute("overflowtarget"));
+  this._list.toolbox = this._toolbar.toolbox;
+  this._list.customizationTarget = this._list;
+
+  let window = this._toolbar.ownerGlobal;
+  if (window.gBrowserInit.delayedStartupFinished) {
+    this.init();
+  } else {
+    Services.obs.addObserver(this, "browser-delayed-startup-finished", false);
+  }
+}
+
+OverflowableToolbar.prototype = {
+  initialized: false,
+  _forceOnOverflow: false,
+
+  observe(aSubject, aTopic, aData) {
+    if (aTopic == "browser-delayed-startup-finished" &&
+        aSubject == this._toolbar.ownerGlobal) {
+      Services.obs.removeObserver(this, "browser-delayed-startup-finished");
+      this.init();
+    }
+  },
+
+  init() {
+    let doc = this._toolbar.ownerDocument;
+    let window = doc.defaultView;
+    window.addEventListener("resize", this);
+    window.gNavToolbox.addEventListener("customizationstarting", this);
+    window.gNavToolbox.addEventListener("aftercustomization", this);
+
+    let chevronId = this._toolbar.getAttribute("overflowbutton");
+    this._chevron = doc.getElementById(chevronId);
+    this._chevron.addEventListener("command", this);
+    this._chevron.addEventListener("dragover", this);
+    this._chevron.addEventListener("dragend", this);
+
+    let panelId = this._toolbar.getAttribute("overflowpanel");
+    this._panel = doc.getElementById(panelId);
+    this._panel.addEventListener("popuphiding", this);
+    CustomizableUIInternal.addPanelCloseListeners(this._panel);
+
+    CustomizableUI.addListener(this);
+
+    // The 'overflow' event may have been fired before init was called.
+    if (this._toolbar.overflowedDuringConstruction) {
+      this.onOverflow(this._toolbar.overflowedDuringConstruction);
+      this._toolbar.overflowedDuringConstruction = null;
+    }
+
+    this.initialized = true;
+  },
+
+  uninit() {
+    this._toolbar.removeEventListener("overflow", this._toolbar);
+    this._toolbar.removeEventListener("underflow", this._toolbar);
+    this._toolbar.removeAttribute("overflowable");
+
+    if (!this.initialized) {
+      Services.obs.removeObserver(this, "browser-delayed-startup-finished");
+      return;
+    }
+
+    this._disable();
+
+    let window = this._toolbar.ownerGlobal;
+    window.removeEventListener("resize", this);
+    window.gNavToolbox.removeEventListener("customizationstarting", this);
+    window.gNavToolbox.removeEventListener("aftercustomization", this);
+    this._chevron.removeEventListener("command", this);
+    this._chevron.removeEventListener("dragover", this);
+    this._chevron.removeEventListener("dragend", this);
+    this._panel.removeEventListener("popuphiding", this);
+    CustomizableUI.removeListener(this);
+    CustomizableUIInternal.removePanelCloseListeners(this._panel);
+  },
+
+  handleEvent(aEvent) {
+    switch (aEvent.type) {
+      case "aftercustomization":
+        this._enable();
+        break;
+      case "command":
+        if (aEvent.target == this._chevron) {
+          this._onClickChevron(aEvent);
+        } else {
+          this._panel.hidePopup();
+        }
+        break;
+      case "customizationstarting":
+        this._disable();
+        break;
+      case "dragover":
+        this._showWithTimeout();
+        break;
+      case "dragend":
+        this._panel.hidePopup();
+        break;
+      case "popuphiding":
+        this._onPanelHiding(aEvent);
+        break;
+      case "resize":
+        this._onResize(aEvent);
+    }
+  },
+
+  show() {
+    if (this._panel.state == "open") {
+      return Promise.resolve();
+    }
+    return new Promise(resolve => {
+      let doc = this._panel.ownerDocument;
+      this._panel.hidden = false;
+      let contextMenu = doc.getElementById(this._panel.getAttribute("context"));
+      gELS.addSystemEventListener(contextMenu, "command", this, true);
+      let anchor = doc.getAnonymousElementByAttribute(this._chevron, "class", "toolbarbutton-icon");
+      this._panel.openPopup(anchor || this._chevron);
+      this._chevron.open = true;
+
+      let overflowableToolbarInstance = this;
+      this._panel.addEventListener("popupshown", function onPopupShown(aEvent) {
+        this.removeEventListener("popupshown", onPopupShown);
+        this.addEventListener("dragover", overflowableToolbarInstance);
+        this.addEventListener("dragend", overflowableToolbarInstance);
+        resolve();
+      });
+    });
+  },
+
+  _onClickChevron(aEvent) {
+    if (this._chevron.open) {
+      this._panel.hidePopup();
+      this._chevron.open = false;
+    } else {
+      this.show();
+    }
+  },
+
+  _onPanelHiding(aEvent) {
+    this._chevron.open = false;
+    this._panel.removeEventListener("dragover", this);
+    this._panel.removeEventListener("dragend", this);
+    let doc = aEvent.target.ownerDocument;
+    let contextMenu = doc.getElementById(this._panel.getAttribute("context"));
+    gELS.removeSystemEventListener(contextMenu, "command", this, true);
+  },
+
+  onOverflow(aEvent) {
+    // The rangeParent check is here because of bug 1111986 and ensuring that
+    // overflow events from the bookmarks toolbar items or similar things that
+    // manage their own overflow don't trigger an overflow on the entire toolbar
+    if (!this._enabled ||
+        (aEvent && aEvent.target != this._toolbar.customizationTarget) ||
+        (aEvent && aEvent.rangeParent))
+      return;
+
+    let child = this._target.lastChild;
+
+    while (child && this._target.scrollLeftMin != this._target.scrollLeftMax) {
+      let prevChild = child.previousSibling;
+
+      if (child.getAttribute("overflows") != "false") {
+        this._collapsed.set(child.id, this._target.clientWidth);
+        child.setAttribute("overflowedItem", true);
+        child.setAttribute("cui-anchorid", this._chevron.id);
+        CustomizableUIInternal.notifyListeners("onWidgetOverflow", child, this._target);
+
+        this._list.insertBefore(child, this._list.firstChild);
+        if (!this._toolbar.hasAttribute("overflowing")) {
+          CustomizableUI.addListener(this);
+        }
+        this._toolbar.setAttribute("overflowing", "true");
+      }
+      child = prevChild;
+    }
+
+    let win = this._target.ownerGlobal;
+    win.UpdateUrlbarSearchSplitterState();
+  },
+
+  _onResize(aEvent) {
+    if (!this._lazyResizeHandler) {
+      this._lazyResizeHandler = new DeferredTask(this._onLazyResize.bind(this),
+                                                 LAZY_RESIZE_INTERVAL_MS);
+    }
+    this._lazyResizeHandler.arm();
+  },
+
+  _moveItemsBackToTheirOrigin(shouldMoveAllItems) {
+    let placements = gPlacements.get(this._toolbar.id);
+    while (this._list.firstChild) {
+      let child = this._list.firstChild;
+      let minSize = this._collapsed.get(child.id);
+
+      if (!shouldMoveAllItems &&
+          minSize &&
+          this._target.clientWidth <= minSize) {
+        return;
+      }
+
+      this._collapsed.delete(child.id);
+      let beforeNodeIndex = placements.indexOf(child.id) + 1;
+      // If this is a skipintoolbarset item, meaning it doesn't occur in the placements list,
+      // we're inserting it at the end. This will mean first-in, first-out (more or less)
+      // leading to as little change in order as possible.
+      if (beforeNodeIndex == 0) {
+        beforeNodeIndex = placements.length;
+      }
+      let inserted = false;
+      for (; beforeNodeIndex < placements.length; beforeNodeIndex++) {
+        let beforeNode = this._target.getElementsByAttribute("id", placements[beforeNodeIndex])[0];
+        if (beforeNode) {
+          this._target.insertBefore(child, beforeNode);
+          inserted = true;
+          break;
+        }
+      }
+      if (!inserted) {
+        this._target.appendChild(child);
+      }
+      child.removeAttribute("cui-anchorid");
+      child.removeAttribute("overflowedItem");
+      CustomizableUIInternal.notifyListeners("onWidgetUnderflow", child, this._target);
+    }
+
+    let win = this._target.ownerGlobal;
+    win.UpdateUrlbarSearchSplitterState();
+
+    if (!this._collapsed.size) {
+      this._toolbar.removeAttribute("overflowing");
+      CustomizableUI.removeListener(this);
+    }
+  },
+
+  _onLazyResize() {
+    if (!this._enabled)
+      return;
+
+    if (this._target.scrollLeftMin != this._target.scrollLeftMax) {
+      this.onOverflow();
+    } else {
+      this._moveItemsBackToTheirOrigin();
+    }
+  },
+
+  _disable() {
+    this._enabled = false;
+    this._moveItemsBackToTheirOrigin(true);
+    if (this._lazyResizeHandler) {
+      this._lazyResizeHandler.disarm();
+    }
+  },
+
+  _enable() {
+    this._enabled = true;
+    this.onOverflow();
+  },
+
+  onWidgetBeforeDOMChange(aNode, aNextNode, aContainer) {
+    if (aContainer != this._target && aContainer != this._list) {
+      return;
+    }
+    // When we (re)move an item, update all the items that come after it in the list
+    // with the minsize *of the item before the to-be-removed node*. This way, we
+    // ensure that we try to move items back as soon as that's possible.
+    if (aNode.parentNode == this._list) {
+      let updatedMinSize;
+      if (aNode.previousSibling) {
+        updatedMinSize = this._collapsed.get(aNode.previousSibling.id);
+      } else {
+        // Force (these) items to try to flow back into the bar:
+        updatedMinSize = 1;
+      }
+      let nextItem = aNode.nextSibling;
+      while (nextItem) {
+        this._collapsed.set(nextItem.id, updatedMinSize);
+        nextItem = nextItem.nextSibling;
+      }
+    }
+  },
+
+  onWidgetAfterDOMChange(aNode, aNextNode, aContainer) {
+    if (aContainer != this._target && aContainer != this._list) {
+      return;
+    }
+
+    let nowInBar = aNode.parentNode == aContainer;
+    let nowOverflowed = aNode.parentNode == this._list;
+    let wasOverflowed = this._collapsed.has(aNode.id);
+
+    // If this wasn't overflowed before...
+    if (!wasOverflowed) {
+      // ... but it is now, then we added to the overflow panel. Exciting stuff:
+      if (nowOverflowed) {
+        // NB: we're guaranteed that it has a previousSibling, because if it didn't,
+        // we would have added it to the toolbar instead. See getOverflowedNextNode.
+        let prevId = aNode.previousSibling.id;
+        let minSize = this._collapsed.get(prevId);
+        this._collapsed.set(aNode.id, minSize);
+        aNode.setAttribute("cui-anchorid", this._chevron.id);
+        aNode.setAttribute("overflowedItem", true);
+        CustomizableUIInternal.notifyListeners("onWidgetOverflow", aNode, this._target);
+      } else if (!nowInBar) {
+        // If it is not overflowed and not in the toolbar, and was not overflowed
+        // either, it moved out of the toolbar. That means there's now space in there!
+        // Let's try to move stuff back:
+        this._moveItemsBackToTheirOrigin(true);
+      }
+      // If it's in the toolbar now, then we don't care. An overflow event may
+      // fire afterwards; that's ok!
+    } else if (!nowOverflowed) {
+      // If it used to be overflowed...
+      // ... and isn't anymore, let's remove our bookkeeping:
+      this._collapsed.delete(aNode.id);
+      aNode.removeAttribute("cui-anchorid");
+      aNode.removeAttribute("overflowedItem");
+      CustomizableUIInternal.notifyListeners("onWidgetUnderflow", aNode, this._target);
+
+      if (!this._collapsed.size) {
+        this._toolbar.removeAttribute("overflowing");
+        CustomizableUI.removeListener(this);
+      }
+    } else if (aNode.previousSibling) {
+      // but if it still is, it must have changed places. Bookkeep:
+      let prevId = aNode.previousSibling.id;
+      let minSize = this._collapsed.get(prevId);
+      this._collapsed.set(aNode.id, minSize);
+    } else {
+      // If it's now the first item in the overflow list,
+      // maybe we can return it:
+      this._moveItemsBackToTheirOrigin();
+    }
+  },
+
+  findOverflowedInsertionPoints(aNode) {
+    let newNodeCanOverflow = aNode.getAttribute("overflows") != "false";
+    let areaId = this._toolbar.id;
+    let placements = gPlacements.get(areaId);
+    let nodeIndex = placements.indexOf(aNode.id);
+    let nodeBeforeNewNodeIsOverflown = false;
+
+    let loopIndex = -1;
+    while (++loopIndex < placements.length) {
+      let nextNodeId = placements[loopIndex];
+      if (loopIndex > nodeIndex) {
+        if (newNodeCanOverflow && this._collapsed.has(nextNodeId)) {
+          let nextNode = this._list.getElementsByAttribute("id", nextNodeId).item(0);
+          if (nextNode) {
+            return [this._list, nextNode];
+          }
+        }
+        if (!nodeBeforeNewNodeIsOverflown || !newNodeCanOverflow) {
+          let nextNode = this._target.getElementsByAttribute("id", nextNodeId).item(0);
+          if (nextNode) {
+            return [this._target, nextNode];
+          }
+        }
+      } else if (loopIndex < nodeIndex && this._collapsed.has(nextNodeId)) {
+        nodeBeforeNewNodeIsOverflown = true;
+      }
+    }
+
+    let containerForAppending = (this._collapsed.size && newNodeCanOverflow) ?
+                                this._list : this._target;
+    return [containerForAppending, null];
+  },
+
+  getContainerFor(aNode) {
+    if (aNode.getAttribute("overflowedItem") == "true") {
+      return this._list;
+    }
+    return this._target;
+  },
+
+  _hideTimeoutId: null,
+  _showWithTimeout() {
+    this.show().then(function() {
+      let window = this._toolbar.ownerGlobal;
+      if (this._hideTimeoutId) {
+        window.clearTimeout(this._hideTimeoutId);
+      }
+      this._hideTimeoutId = window.setTimeout(() => {
+        if (!this._panel.firstChild.matches(":hover")) {
+          this._panel.hidePopup();
+        }
+      }, OVERFLOW_PANEL_HIDE_DELAY_MS);
+    }.bind(this));
+  },
+};
+
+CustomizableUIInternal.initialize();
diff --git a/application/basilisk/components/customizableui/CustomizableWidgets.jsm b/application/basilisk/components/customizableui/CustomizableWidgets.jsm
new file mode 100644
index 000000000..e3c55e551
--- /dev/null
+++ b/application/basilisk/components/customizableui/CustomizableWidgets.jsm
@@ -0,0 +1,1240 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;
+
+this.EXPORTED_SYMBOLS = ["CustomizableWidgets"];
+
+Cu.import("resource:///modules/CustomizableUI.jsm");
+Cu.import("resource://gre/modules/Services.jsm");
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "BrowserUITelemetry",
+  "resource:///modules/BrowserUITelemetry.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PlacesUtils",
+  "resource://gre/modules/PlacesUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PlacesUIUtils",
+  "resource:///modules/PlacesUIUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "RecentlyClosedTabsAndWindowsMenuUtils",
+  "resource:///modules/sessionstore/RecentlyClosedTabsAndWindowsMenuUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "ShortcutUtils",
+  "resource://gre/modules/ShortcutUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "CharsetMenu",
+  "resource://gre/modules/CharsetMenu.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PrivateBrowsingUtils",
+  "resource://gre/modules/PrivateBrowsingUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "SyncedTabs",
+  "resource://services-sync/SyncedTabs.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "ContextualIdentityService",
+  "resource://gre/modules/ContextualIdentityService.jsm");
+
+XPCOMUtils.defineLazyGetter(this, "CharsetBundle", function() {
+  const kCharsetBundle = "chrome://global/locale/charsetMenu.properties";
+  return Services.strings.createBundle(kCharsetBundle);
+});
+XPCOMUtils.defineLazyGetter(this, "BrandBundle", function() {
+  const kBrandBundle = "chrome://branding/locale/brand.properties";
+  return Services.strings.createBundle(kBrandBundle);
+});
+
+const kNSXUL = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
+const kPrefCustomizationDebug = "browser.uiCustomization.debug";
+const kWidePanelItemClass = "panel-wide-item";
+
+XPCOMUtils.defineLazyGetter(this, "log", () => {
+  let scope = {};
+  Cu.import("resource://gre/modules/Console.jsm", scope);
+  let debug;
+  try {
+    debug = Services.prefs.getBoolPref(kPrefCustomizationDebug);
+  } catch (ex) {}
+  let consoleOptions = {
+    maxLogLevel: debug ? "all" : "log",
+    prefix: "CustomizableWidgets",
+  };
+  return new scope.ConsoleAPI(consoleOptions);
+});
+
+
+
+function setAttributes(aNode, aAttrs) {
+  let doc = aNode.ownerDocument;
+  for (let [name, value] of Object.entries(aAttrs)) {
+    if (!value) {
+      if (aNode.hasAttribute(name))
+        aNode.removeAttribute(name);
+    } else {
+      if (name == "shortcutId") {
+        continue;
+      }
+      if (name == "label" || name == "tooltiptext") {
+        let stringId = (typeof value == "string") ? value : name;
+        let additionalArgs = [];
+        if (aAttrs.shortcutId) {
+          let shortcut = doc.getElementById(aAttrs.shortcutId);
+          if (shortcut) {
+            additionalArgs.push(ShortcutUtils.prettifyShortcut(shortcut));
+          }
+        }
+        value = CustomizableUI.getLocalizedProperty({id: aAttrs.id}, stringId, additionalArgs);
+      }
+      aNode.setAttribute(name, value);
+    }
+  }
+}
+
+function updateCombinedWidgetStyle(aNode, aArea, aModifyCloseMenu) {
+  let inPanel = (aArea == CustomizableUI.AREA_PANEL);
+  let cls = inPanel ? "panel-combined-button" : "toolbarbutton-1 toolbarbutton-combined";
+  let attrs = {class: cls};
+  if (aModifyCloseMenu) {
+    attrs.closemenu = inPanel ? "none" : null;
+  }
+  for (let i = 0, l = aNode.childNodes.length; i < l; ++i) {
+    if (aNode.childNodes[i].localName == "separator")
+      continue;
+    setAttributes(aNode.childNodes[i], attrs);
+  }
+}
+
+function fillSubviewFromMenuItems(aMenuItems, aSubview) {
+  let attrs = ["oncommand", "onclick", "label", "key", "disabled",
+               "command", "observes", "hidden", "class", "origin",
+               "image", "checked"];
+
+  let doc = aSubview.ownerDocument;
+  let fragment = doc.createDocumentFragment();
+  for (let menuChild of aMenuItems) {
+    if (menuChild.hidden)
+      continue;
+
+    let subviewItem;
+    if (menuChild.localName == "menuseparator") {
+      // Don't insert duplicate or leading separators. This can happen if there are
+      // menus (which we don't copy) above the separator.
+      if (!fragment.lastChild || fragment.lastChild.localName == "menuseparator") {
+        continue;
+      }
+      subviewItem = doc.createElementNS(kNSXUL, "menuseparator");
+    } else if (menuChild.localName == "menuitem") {
+      subviewItem = doc.createElementNS(kNSXUL, "toolbarbutton");
+      CustomizableUI.addShortcut(menuChild, subviewItem);
+
+      let item = menuChild;
+      if (!item.hasAttribute("onclick")) {
+        subviewItem.addEventListener("click", event => {
+          let newEvent = new doc.defaultView.MouseEvent(event.type, event);
+          item.dispatchEvent(newEvent);
+        });
+      }
+
+      if (!item.hasAttribute("oncommand")) {
+        subviewItem.addEventListener("command", event => {
+          let newEvent = doc.createEvent("XULCommandEvent");
+          newEvent.initCommandEvent(
+            event.type, event.bubbles, event.cancelable, event.view,
+            event.detail, event.ctrlKey, event.altKey, event.shiftKey,
+            event.metaKey, event.sourceEvent);
+          item.dispatchEvent(newEvent);
+        });
+      }
+    } else {
+      continue;
+    }
+    for (let attr of attrs) {
+      let attrVal = menuChild.getAttribute(attr);
+      if (attrVal)
+        subviewItem.setAttribute(attr, attrVal);
+    }
+    // We do this after so the .subviewbutton class doesn't get overriden.
+    if (menuChild.localName == "menuitem") {
+      subviewItem.classList.add("subviewbutton");
+    }
+    fragment.appendChild(subviewItem);
+  }
+  aSubview.appendChild(fragment);
+}
+
+function clearSubview(aSubview) {
+  let parent = aSubview.parentNode;
+  // We'll take the container out of the document before cleaning it out
+  // to avoid reflowing each time we remove something.
+  parent.removeChild(aSubview);
+
+  while (aSubview.firstChild) {
+    aSubview.firstChild.remove();
+  }
+
+  parent.appendChild(aSubview);
+}
+
+const CustomizableWidgets = [
+  {
+    id: "history-panelmenu",
+    type: "view",
+    viewId: "PanelUI-history",
+    shortcutId: "key_gotoHistory",
+    tooltiptext: "history-panelmenu.tooltiptext2",
+    defaultArea: CustomizableUI.AREA_PANEL,
+    onViewShowing(aEvent) {
+      // Populate our list of history
+      const kMaxResults = 15;
+      let doc = aEvent.target.ownerDocument;
+      let win = doc.defaultView;
+
+      let options = PlacesUtils.history.getNewQueryOptions();
+      options.excludeQueries = true;
+      options.queryType = options.QUERY_TYPE_HISTORY;
+      options.sortingMode = options.SORT_BY_DATE_DESCENDING;
+      options.maxResults = kMaxResults;
+      let query = PlacesUtils.history.getNewQuery();
+
+      let items = doc.getElementById("PanelUI-historyItems");
+      // Clear previous history items.
+      while (items.firstChild) {
+        items.firstChild.remove();
+      }
+
+      // Get all statically placed buttons to supply them with keyboard shortcuts.
+      let staticButtons = items.parentNode.getElementsByTagNameNS(kNSXUL, "toolbarbutton");
+      for (let i = 0, l = staticButtons.length; i < l; ++i)
+        CustomizableUI.addShortcut(staticButtons[i]);
+
+      PlacesUtils.history.QueryInterface(Ci.nsPIPlacesDatabase)
+                         .asyncExecuteLegacyQueries([query], 1, options, {
+        handleResult(aResultSet) {
+          let onItemCommand = function(aItemCommandEvent) {
+            // Only handle the click event for middle clicks, we're using the command
+            // event otherwise.
+            if (aItemCommandEvent.type == "click" &&
+                aItemCommandEvent.button != 1) {
+              return;
+            }
+            let item = aItemCommandEvent.target;
+            win.openUILink(item.getAttribute("targetURI"), aItemCommandEvent);
+            CustomizableUI.hidePanelForNode(item);
+          };
+          let fragment = doc.createDocumentFragment();
+          let row;
+          while ((row = aResultSet.getNextRow())) {
+            let uri = row.getResultByIndex(1);
+            let title = row.getResultByIndex(2);
+            let icon = row.getResultByIndex(6);
+
+            let item = doc.createElementNS(kNSXUL, "toolbarbutton");
+            item.setAttribute("label", title || uri);
+            item.setAttribute("targetURI", uri);
+            item.setAttribute("class", "subviewbutton");
+            item.addEventListener("command", onItemCommand);
+            item.addEventListener("click", onItemCommand);
+            if (icon) {
+              let iconURL = "moz-anno:favicon:" + icon;
+              item.setAttribute("image", iconURL);
+            }
+            fragment.appendChild(item);
+          }
+          items.appendChild(fragment);
+        },
+        handleError(aError) {
+          log.debug("History view tried to show but had an error: " + aError);
+        },
+        handleCompletion(aReason) {
+          log.debug("History view is being shown!");
+        },
+      });
+
+      let recentlyClosedTabs = doc.getElementById("PanelUI-recentlyClosedTabs");
+      while (recentlyClosedTabs.firstChild) {
+        recentlyClosedTabs.removeChild(recentlyClosedTabs.firstChild);
+      }
+
+      let recentlyClosedWindows = doc.getElementById("PanelUI-recentlyClosedWindows");
+      while (recentlyClosedWindows.firstChild) {
+        recentlyClosedWindows.removeChild(recentlyClosedWindows.firstChild);
+      }
+
+      let utils = RecentlyClosedTabsAndWindowsMenuUtils;
+      let tabsFragment = utils.getTabsFragment(doc.defaultView, "toolbarbutton", true,
+                                               "menuRestoreAllTabsSubview.label");
+      let separator = doc.getElementById("PanelUI-recentlyClosedTabs-separator");
+      let elementCount = tabsFragment.childElementCount;
+      separator.hidden = !elementCount;
+      while (--elementCount >= 0) {
+        let element = tabsFragment.children[elementCount];
+        CustomizableUI.addShortcut(element);
+        element.classList.add("subviewbutton", "cui-withicon");
+      }
+      recentlyClosedTabs.appendChild(tabsFragment);
+
+      let windowsFragment = utils.getWindowsFragment(doc.defaultView, "toolbarbutton", true,
+                                                     "menuRestoreAllWindowsSubview.label");
+      separator = doc.getElementById("PanelUI-recentlyClosedWindows-separator");
+      elementCount = windowsFragment.childElementCount;
+      separator.hidden = !elementCount;
+      while (--elementCount >= 0) {
+        let element = windowsFragment.children[elementCount];
+        CustomizableUI.addShortcut(element);
+        element.classList.add("subviewbutton", "cui-withicon");
+      }
+      recentlyClosedWindows.appendChild(windowsFragment);
+    },
+    onCreated(aNode) {
+      // Middle clicking recently closed items won't close the panel - cope:
+      let onRecentlyClosedClick = function(aEvent) {
+        if (aEvent.button == 1) {
+          CustomizableUI.hidePanelForNode(this);
+        }
+      };
+      let doc = aNode.ownerDocument;
+      let recentlyClosedTabs = doc.getElementById("PanelUI-recentlyClosedTabs");
+      let recentlyClosedWindows = doc.getElementById("PanelUI-recentlyClosedWindows");
+      recentlyClosedTabs.addEventListener("click", onRecentlyClosedClick);
+      recentlyClosedWindows.addEventListener("click", onRecentlyClosedClick);
+    },
+    onViewHiding(aEvent) {
+      log.debug("History view is being hidden!");
+    }
+  }, {
+    id: "sync-button",
+    label: "remotetabs-panelmenu.label",
+    tooltiptext: "remotetabs-panelmenu.tooltiptext2",
+    type: "view",
+    viewId: "PanelUI-remotetabs",
+    defaultArea: CustomizableUI.AREA_PANEL,
+    deckIndices: {
+      DECKINDEX_TABS: 0,
+      DECKINDEX_TABSDISABLED: 1,
+      DECKINDEX_FETCHING: 2,
+      DECKINDEX_NOCLIENTS: 3,
+    },
+    onCreated(aNode) {
+      // Add an observer to the button so we get the animation during sync.
+      // (Note the observer sets many attributes, including label and
+      // tooltiptext, but we only want the 'syncstatus' attribute for the
+      // animation)
+      let doc = aNode.ownerDocument;
+      let obnode = doc.createElementNS(kNSXUL, "observes");
+      obnode.setAttribute("element", "sync-status");
+      obnode.setAttribute("attribute", "syncstatus");
+      aNode.appendChild(obnode);
+
+      // A somewhat complicated dance to format the mobilepromo label.
+      let bundle = doc.getElementById("bundle_browser");
+      let formatArgs = ["android", "ios"].map(os => {
+        let link = doc.createElement("label");
+        link.textContent = bundle.getString(`appMenuRemoteTabs.mobilePromo.${os}`);
+        link.setAttribute("mobile-promo-os", os);
+        link.className = "text-link remotetabs-promo-link";
+        return link.outerHTML;
+      });
+      let promoParentElt = doc.getElementById("PanelUI-remotetabs-mobile-promo");
+      // Put it all together...
+      let contents = bundle.getFormattedString("appMenuRemoteTabs.mobilePromo.text2", formatArgs);
+      promoParentElt.innerHTML = contents;
+      // We manually manage the "click" event to open the promo links because
+      // allowing the "text-link" widget handle it has 2 problems: (1) it only
+      // supports button 0 and (2) it's tricky to intercept when it does the
+      // open and auto-close the panel. (1) can probably be fixed, but (2) is
+      // trickier without hard-coding here the knowledge of exactly what buttons
+      // it does support.
+      // So we allow left and middle clicks to open the link in a new tab and
+      // close the panel; not setting a "href" attribute prevents the text-link
+      // widget handling it, and we build the final URL in the click handler to
+      // make testing easier (ie, so tests can change the pref after the links
+      // were created and have the new pref value used.)
+      promoParentElt.addEventListener("click", e => {
+        let os = e.target.getAttribute("mobile-promo-os");
+        if (!os || e.button > 1) {
+          return;
+        }
+        let link = Services.prefs.getCharPref(`identity.mobilepromo.${os}`) + "synced-tabs";
+        doc.defaultView.openUILinkIn(link, "tab");
+        CustomizableUI.hidePanelForNode(e.target);
+      });
+    },
+    onViewShowing(aEvent) {
+      let doc = aEvent.target.ownerDocument;
+      this._tabsList = doc.getElementById("PanelUI-remotetabs-tabslist");
+      Services.obs.addObserver(this, SyncedTabs.TOPIC_TABS_CHANGED, false);
+
+      if (SyncedTabs.isConfiguredToSyncTabs) {
+        if (SyncedTabs.hasSyncedThisSession) {
+          this.setDeckIndex(this.deckIndices.DECKINDEX_TABS);
+        } else {
+          // Sync hasn't synced tabs yet, so show the "fetching" panel.
+          this.setDeckIndex(this.deckIndices.DECKINDEX_FETCHING);
+        }
+        // force a background sync.
+        SyncedTabs.syncTabs().catch(ex => {
+          Cu.reportError(ex);
+        });
+        // show the current list - it will be updated by our observer.
+        this._showTabs();
+      } else {
+        // not configured to sync tabs, so no point updating the list.
+        this.setDeckIndex(this.deckIndices.DECKINDEX_TABSDISABLED);
+      }
+    },
+    onViewHiding() {
+      Services.obs.removeObserver(this, SyncedTabs.TOPIC_TABS_CHANGED);
+      this._tabsList = null;
+    },
+    _tabsList: null,
+    observe(subject, topic, data) {
+      switch (topic) {
+        case SyncedTabs.TOPIC_TABS_CHANGED:
+          this._showTabs();
+          break;
+        default:
+          break;
+      }
+    },
+    setDeckIndex(index) {
+      let deck = this._tabsList.ownerDocument.getElementById("PanelUI-remotetabs-deck");
+      // We call setAttribute instead of relying on the XBL property setter due
+      // to things going wrong when we try and set the index before the XBL
+      // binding has been created - see bug 1241851 for the gory details.
+      deck.setAttribute("selectedIndex", index);
+    },
+
+    _showTabsPromise: Promise.resolve(),
+    // Update the tab list after any existing in-flight updates are complete.
+    _showTabs() {
+      this._showTabsPromise = this._showTabsPromise.then(() => {
+        return this.__showTabs();
+      });
+    },
+    // Return a new promise to update the tab list.
+    __showTabs() {
+      let doc = this._tabsList.ownerDocument;
+      return SyncedTabs.getTabClients().then(clients => {
+        // The view may have been hidden while the promise was resolving.
+        if (!this._tabsList) {
+          return;
+        }
+        if (clients.length === 0 && !SyncedTabs.hasSyncedThisSession) {
+          // the "fetching tabs" deck is being shown - let's leave it there.
+          // When that first sync completes we'll be notified and update.
+          return;
+        }
+
+        if (clients.length === 0) {
+          this.setDeckIndex(this.deckIndices.DECKINDEX_NOCLIENTS);
+          return;
+        }
+
+        this.setDeckIndex(this.deckIndices.DECKINDEX_TABS);
+        this._clearTabList();
+        SyncedTabs.sortTabClientsByLastUsed(clients, 50 /* maxTabs */);
+        let fragment = doc.createDocumentFragment();
+
+        for (let client of clients) {
+          // add a menu separator for all clients other than the first.
+          if (fragment.lastChild) {
+            let separator = doc.createElementNS(kNSXUL, "menuseparator");
+            fragment.appendChild(separator);
+          }
+          this._appendClient(client, fragment);
+        }
+        this._tabsList.appendChild(fragment);
+      }).catch(err => {
+        Cu.reportError(err);
+      }).then(() => {
+        // an observer for tests.
+        Services.obs.notifyObservers(null, "synced-tabs-menu:test:tabs-updated", null);
+      });
+    },
+    _clearTabList() {
+      let list = this._tabsList;
+      while (list.lastChild) {
+        list.lastChild.remove();
+      }
+    },
+    _showNoClientMessage() {
+      this._appendMessageLabel("notabslabel");
+    },
+    _appendMessageLabel(messageAttr, appendTo = null) {
+      if (!appendTo) {
+        appendTo = this._tabsList;
+      }
+      let message = this._tabsList.getAttribute(messageAttr);
+      let doc = this._tabsList.ownerDocument;
+      let messageLabel = doc.createElementNS(kNSXUL, "label");
+      messageLabel.textContent = message;
+      appendTo.appendChild(messageLabel);
+      return messageLabel;
+    },
+    _appendClient(client, attachFragment) {
+      let doc = attachFragment.ownerDocument;
+      // Create the element for the remote client.
+      let clientItem = doc.createElementNS(kNSXUL, "label");
+      clientItem.setAttribute("itemtype", "client");
+      let window = doc.defaultView;
+      clientItem.setAttribute("tooltiptext",
+        window.gSyncUI.formatLastSyncDate(new Date(client.lastModified)));
+      clientItem.textContent = client.name;
+
+      attachFragment.appendChild(clientItem);
+
+      if (client.tabs.length == 0) {
+        let label = this._appendMessageLabel("notabsforclientlabel", attachFragment);
+        label.setAttribute("class", "PanelUI-remotetabs-notabsforclient-label");
+      } else {
+        for (let tab of client.tabs) {
+          let tabEnt = this._createTabElement(doc, tab);
+          attachFragment.appendChild(tabEnt);
+        }
+      }
+    },
+    _createTabElement(doc, tabInfo) {
+      let item = doc.createElementNS(kNSXUL, "toolbarbutton");
+      let tooltipText = (tabInfo.title ? tabInfo.title + "\n" : "") + tabInfo.url;
+      item.setAttribute("itemtype", "tab");
+      item.setAttribute("class", "subviewbutton");
+      item.setAttribute("targetURI", tabInfo.url);
+      item.setAttribute("label", tabInfo.title != "" ? tabInfo.title : tabInfo.url);
+      item.setAttribute("image", tabInfo.icon);
+      item.setAttribute("tooltiptext", tooltipText);
+      // We need to use "click" instead of "command" here so openUILink
+      // respects different buttons (eg, to open in a new tab).
+      item.addEventListener("click", e => {
+        doc.defaultView.openUILink(tabInfo.url, e);
+        CustomizableUI.hidePanelForNode(item);
+        BrowserUITelemetry.countSyncedTabEvent("open", "toolbarbutton-subview");
+      });
+      return item;
+    },
+  }, {
+    id: "privatebrowsing-button",
+    shortcutId: "key_privatebrowsing",
+    defaultArea: CustomizableUI.AREA_PANEL,
+    onCommand(e) {
+      let win = e.target.ownerGlobal;
+      win.OpenBrowserWindow({private: true});
+    }
+  }, {
+    id: "save-page-button",
+    shortcutId: "key_savePage",
+    tooltiptext: "save-page-button.tooltiptext3",
+    defaultArea: CustomizableUI.AREA_PANEL,
+    onCommand(aEvent) {
+      let win = aEvent.target.ownerGlobal;
+      win.saveBrowser(win.gBrowser.selectedBrowser);
+    }
+  }, {
+    id: "find-button",
+    shortcutId: "key_find",
+    tooltiptext: "find-button.tooltiptext3",
+    defaultArea: CustomizableUI.AREA_PANEL,
+    onCommand(aEvent) {
+      let win = aEvent.target.ownerGlobal;
+      if (win.gFindBar) {
+        win.gFindBar.onFindCommand();
+      }
+    }
+  }, {
+    id: "open-file-button",
+    shortcutId: "openFileKb",
+    tooltiptext: "open-file-button.tooltiptext3",
+    defaultArea: CustomizableUI.AREA_PANEL,
+    onCommand(aEvent) {
+      let win = aEvent.target.ownerGlobal;
+      win.BrowserOpenFileWindow();
+    }
+  }, {
+    id: "sidebar-button",
+    type: "view",
+    viewId: "PanelUI-sidebar",
+    tooltiptext: "sidebar-button.tooltiptext2",
+    onViewShowing(aEvent) {
+      // Populate the subview with whatever menuitems are in the
+      // sidebar menu. We skip menu elements, because the menu panel has no way
+      // of dealing with those right now.
+      let doc = aEvent.target.ownerDocument;
+      let menu = doc.getElementById("viewSidebarMenu");
+
+      // First clear any existing menuitems then populate. Add it to the
+      // standard menu first, then copy all sidebar options to the panel.
+      let sidebarItems = doc.getElementById("PanelUI-sidebarItems");
+      clearSubview(sidebarItems);
+      fillSubviewFromMenuItems([...menu.children], sidebarItems);
+    }
+  }, {
+    id: "add-ons-button",
+    shortcutId: "key_openAddons",
+    tooltiptext: "add-ons-button.tooltiptext3",
+    defaultArea: CustomizableUI.AREA_PANEL,
+    onCommand(aEvent) {
+      let win = aEvent.target.ownerGlobal;
+      win.BrowserOpenAddonsMgr();
+    }
+  }, {
+    id: "zoom-controls",
+    type: "custom",
+    tooltiptext: "zoom-controls.tooltiptext2",
+    defaultArea: CustomizableUI.AREA_PANEL,
+    onBuild(aDocument) {
+      const kPanelId = "PanelUI-popup";
+      let areaType = CustomizableUI.getAreaType(this.currentArea);
+      let inPanel = areaType == CustomizableUI.TYPE_MENU_PANEL;
+      let inToolbar = areaType == CustomizableUI.TYPE_TOOLBAR;
+
+      let buttons = [{
+        id: "zoom-out-button",
+        command: "cmd_fullZoomReduce",
+        label: true,
+        tooltiptext: "tooltiptext2",
+        shortcutId: "key_fullZoomReduce",
+      }, {
+        id: "zoom-reset-button",
+        command: "cmd_fullZoomReset",
+        tooltiptext: "tooltiptext2",
+        shortcutId: "key_fullZoomReset",
+      }, {
+        id: "zoom-in-button",
+        command: "cmd_fullZoomEnlarge",
+        label: true,
+        tooltiptext: "tooltiptext2",
+        shortcutId: "key_fullZoomEnlarge",
+      }];
+
+      let node = aDocument.createElementNS(kNSXUL, "toolbaritem");
+      node.setAttribute("id", "zoom-controls");
+      node.setAttribute("label", CustomizableUI.getLocalizedProperty(this, "label"));
+      node.setAttribute("title", CustomizableUI.getLocalizedProperty(this, "tooltiptext"));
+      // Set this as an attribute in addition to the property to make sure we can style correctly.
+      node.setAttribute("removable", "true");
+      node.classList.add("chromeclass-toolbar-additional");
+      node.classList.add("toolbaritem-combined-buttons");
+      node.classList.add(kWidePanelItemClass);
+
+      buttons.forEach(function(aButton, aIndex) {
+        if (aIndex != 0)
+          node.appendChild(aDocument.createElementNS(kNSXUL, "separator"));
+        let btnNode = aDocument.createElementNS(kNSXUL, "toolbarbutton");
+        setAttributes(btnNode, aButton);
+        node.appendChild(btnNode);
+      });
+
+      // The middle node is the 'Reset Zoom' button.
+      let zoomResetButton = node.childNodes[2];
+      let window = aDocument.defaultView;
+      function updateZoomResetButton() {
+        let updateDisplay = true;
+        // Label should always show 100% in customize mode, so don't update:
+        if (aDocument.documentElement.hasAttribute("customizing")) {
+          updateDisplay = false;
+        }
+        // XXXgijs in some tests we get called very early, and there's no docShell on the
+        // tabbrowser. This breaks the zoom toolkit code (see bug 897410). Don't let that happen:
+        let zoomFactor = 100;
+        try {
+          zoomFactor = Math.round(window.ZoomManager.zoom * 100);
+        } catch (e) {}
+        zoomResetButton.setAttribute("label", CustomizableUI.getLocalizedProperty(
+          buttons[1], "label", [updateDisplay ? zoomFactor : 100]
+        ));
+      }
+
+      // Register ourselves with the service so we know when the zoom prefs change.
+      Services.obs.addObserver(updateZoomResetButton, "browser-fullZoom:zoomChange", false);
+      Services.obs.addObserver(updateZoomResetButton, "browser-fullZoom:zoomReset", false);
+      Services.obs.addObserver(updateZoomResetButton, "browser-fullZoom:location-change", false);
+
+      if (inPanel) {
+        let panel = aDocument.getElementById(kPanelId);
+        panel.addEventListener("popupshowing", updateZoomResetButton);
+      } else {
+        if (inToolbar) {
+          let container = window.gBrowser.tabContainer;
+          container.addEventListener("TabSelect", updateZoomResetButton);
+        }
+        updateZoomResetButton();
+      }
+      updateCombinedWidgetStyle(node, this.currentArea, true);
+
+      let listener = {
+        onWidgetAdded: function(aWidgetId, aArea, aPosition) {
+          if (aWidgetId != this.id)
+            return;
+
+          updateCombinedWidgetStyle(node, aArea, true);
+          updateZoomResetButton();
+
+          let newAreaType = CustomizableUI.getAreaType(aArea);
+          if (newAreaType == CustomizableUI.TYPE_MENU_PANEL) {
+            let panel = aDocument.getElementById(kPanelId);
+            panel.addEventListener("popupshowing", updateZoomResetButton);
+          } else if (newAreaType == CustomizableUI.TYPE_TOOLBAR) {
+            let container = window.gBrowser.tabContainer;
+            container.addEventListener("TabSelect", updateZoomResetButton);
+          }
+        }.bind(this),
+
+        onWidgetRemoved: function(aWidgetId, aPrevArea) {
+          if (aWidgetId != this.id)
+            return;
+
+          let formerAreaType = CustomizableUI.getAreaType(aPrevArea);
+          if (formerAreaType == CustomizableUI.TYPE_MENU_PANEL) {
+            let panel = aDocument.getElementById(kPanelId);
+            panel.removeEventListener("popupshowing", updateZoomResetButton);
+          } else if (formerAreaType == CustomizableUI.TYPE_TOOLBAR) {
+            let container = window.gBrowser.tabContainer;
+            container.removeEventListener("TabSelect", updateZoomResetButton);
+          }
+
+          // When a widget is demoted to the palette ('removed'), it's visual
+          // style should change.
+          updateCombinedWidgetStyle(node, null, true);
+          updateZoomResetButton();
+        }.bind(this),
+
+        onWidgetReset: function(aWidgetNode) {
+          if (aWidgetNode != node)
+            return;
+          updateCombinedWidgetStyle(node, this.currentArea, true);
+          updateZoomResetButton();
+        }.bind(this),
+
+        onWidgetUndoMove: function(aWidgetNode) {
+          if (aWidgetNode != node)
+            return;
+          updateCombinedWidgetStyle(node, this.currentArea, true);
+          updateZoomResetButton();
+        }.bind(this),
+
+        onWidgetMoved: function(aWidgetId, aArea) {
+          if (aWidgetId != this.id)
+            return;
+          updateCombinedWidgetStyle(node, aArea, true);
+          updateZoomResetButton();
+        }.bind(this),
+
+        onWidgetInstanceRemoved: function(aWidgetId, aDoc) {
+          if (aWidgetId != this.id || aDoc != aDocument)
+            return;
+
+          CustomizableUI.removeListener(listener);
+          Services.obs.removeObserver(updateZoomResetButton, "browser-fullZoom:zoomChange");
+          Services.obs.removeObserver(updateZoomResetButton, "browser-fullZoom:zoomReset");
+          Services.obs.removeObserver(updateZoomResetButton, "browser-fullZoom:location-change");
+          let panel = aDoc.getElementById(kPanelId);
+          panel.removeEventListener("popupshowing", updateZoomResetButton);
+          let container = aDoc.defaultView.gBrowser.tabContainer;
+          container.removeEventListener("TabSelect", updateZoomResetButton);
+        }.bind(this),
+
+        onCustomizeStart(aWindow) {
+          if (aWindow.document == aDocument) {
+            updateZoomResetButton();
+          }
+        },
+
+        onCustomizeEnd(aWindow) {
+          if (aWindow.document == aDocument) {
+            updateZoomResetButton();
+          }
+        },
+
+        onWidgetDrag: function(aWidgetId, aArea) {
+          if (aWidgetId != this.id)
+            return;
+          aArea = aArea || this.currentArea;
+          updateCombinedWidgetStyle(node, aArea, true);
+        }.bind(this)
+      };
+      CustomizableUI.addListener(listener);
+
+      return node;
+    }
+  }, {
+    id: "edit-controls",
+    type: "custom",
+    tooltiptext: "edit-controls.tooltiptext2",
+    defaultArea: CustomizableUI.AREA_PANEL,
+    onBuild(aDocument) {
+      let buttons = [{
+        id: "cut-button",
+        command: "cmd_cut",
+        label: true,
+        tooltiptext: "tooltiptext2",
+        shortcutId: "key_cut",
+      }, {
+        id: "copy-button",
+        command: "cmd_copy",
+        label: true,
+        tooltiptext: "tooltiptext2",
+        shortcutId: "key_copy",
+      }, {
+        id: "paste-button",
+        command: "cmd_paste",
+        label: true,
+        tooltiptext: "tooltiptext2",
+        shortcutId: "key_paste",
+      }];
+
+      let node = aDocument.createElementNS(kNSXUL, "toolbaritem");
+      node.setAttribute("id", "edit-controls");
+      node.setAttribute("label", CustomizableUI.getLocalizedProperty(this, "label"));
+      node.setAttribute("title", CustomizableUI.getLocalizedProperty(this, "tooltiptext"));
+      // Set this as an attribute in addition to the property to make sure we can style correctly.
+      node.setAttribute("removable", "true");
+      node.classList.add("chromeclass-toolbar-additional");
+      node.classList.add("toolbaritem-combined-buttons");
+      node.classList.add(kWidePanelItemClass);
+
+      buttons.forEach(function(aButton, aIndex) {
+        if (aIndex != 0)
+          node.appendChild(aDocument.createElementNS(kNSXUL, "separator"));
+        let btnNode = aDocument.createElementNS(kNSXUL, "toolbarbutton");
+        setAttributes(btnNode, aButton);
+        node.appendChild(btnNode);
+      });
+
+      updateCombinedWidgetStyle(node, this.currentArea);
+
+      let listener = {
+        onWidgetAdded: function(aWidgetId, aArea, aPosition) {
+          if (aWidgetId != this.id)
+            return;
+          updateCombinedWidgetStyle(node, aArea);
+        }.bind(this),
+
+        onWidgetRemoved: function(aWidgetId, aPrevArea) {
+          if (aWidgetId != this.id)
+            return;
+          // When a widget is demoted to the palette ('removed'), it's visual
+          // style should change.
+          updateCombinedWidgetStyle(node);
+        }.bind(this),
+
+        onWidgetReset: function(aWidgetNode) {
+          if (aWidgetNode != node)
+            return;
+          updateCombinedWidgetStyle(node, this.currentArea);
+        }.bind(this),
+
+        onWidgetUndoMove: function(aWidgetNode) {
+          if (aWidgetNode != node)
+            return;
+          updateCombinedWidgetStyle(node, this.currentArea);
+        }.bind(this),
+
+        onWidgetMoved: function(aWidgetId, aArea) {
+          if (aWidgetId != this.id)
+            return;
+          updateCombinedWidgetStyle(node, aArea);
+        }.bind(this),
+
+        onWidgetInstanceRemoved: function(aWidgetId, aDoc) {
+          if (aWidgetId != this.id || aDoc != aDocument)
+            return;
+          CustomizableUI.removeListener(listener);
+        }.bind(this),
+
+        onWidgetDrag: function(aWidgetId, aArea) {
+          if (aWidgetId != this.id)
+            return;
+          aArea = aArea || this.currentArea;
+          updateCombinedWidgetStyle(node, aArea);
+        }.bind(this)
+      };
+      CustomizableUI.addListener(listener);
+
+      return node;
+    }
+  },
+  {
+    id: "feed-button",
+    type: "view",
+    viewId: "PanelUI-feeds",
+    tooltiptext: "feed-button.tooltiptext2",
+    defaultArea: CustomizableUI.AREA_PANEL,
+    onClick(aEvent) {
+      let win = aEvent.target.ownerGlobal;
+      let feeds = win.gBrowser.selectedBrowser.feeds;
+
+      // Here, we only care about the case where we have exactly 1 feed and the
+      // user clicked...
+      let isClick = (aEvent.button == 0 || aEvent.button == 1);
+      if (feeds && feeds.length == 1 && isClick) {
+        aEvent.preventDefault();
+        aEvent.stopPropagation();
+        win.FeedHandler.subscribeToFeed(feeds[0].href, aEvent);
+        CustomizableUI.hidePanelForNode(aEvent.target);
+      }
+    },
+    onViewShowing(aEvent) {
+      let doc = aEvent.target.ownerDocument;
+      let container = doc.getElementById("PanelUI-feeds");
+      let gotView = doc.defaultView.FeedHandler.buildFeedList(container, true);
+
+      // For no feeds or only a single one, don't show the panel.
+      if (!gotView) {
+        aEvent.preventDefault();
+        aEvent.stopPropagation();
+      }
+    },
+    onCreated(node) {
+      let win = node.ownerGlobal;
+      let selectedBrowser = win.gBrowser.selectedBrowser;
+      let feeds = selectedBrowser && selectedBrowser.feeds;
+      if (!feeds || !feeds.length) {
+        node.setAttribute("disabled", "true");
+      }
+    }
+  }, {
+    id: "characterencoding-button",
+    label: "characterencoding-button2.label",
+    type: "view",
+    viewId: "PanelUI-characterEncodingView",
+    tooltiptext: "characterencoding-button2.tooltiptext",
+    defaultArea: CustomizableUI.AREA_PANEL,
+    maybeDisableMenu(aDocument) {
+      let window = aDocument.defaultView;
+      return !(window.gBrowser &&
+               window.gBrowser.selectedBrowser.mayEnableCharacterEncodingMenu);
+    },
+    populateList(aDocument, aContainerId, aSection) {
+      let containerElem = aDocument.getElementById(aContainerId);
+
+      containerElem.addEventListener("command", this.onCommand);
+
+      let list = this.charsetInfo[aSection];
+
+      for (let item of list) {
+        let elem = aDocument.createElementNS(kNSXUL, "toolbarbutton");
+        elem.setAttribute("label", item.label);
+        elem.setAttribute("type", "checkbox");
+        elem.section = aSection;
+        elem.value = item.value;
+        elem.setAttribute("class", "subviewbutton");
+        containerElem.appendChild(elem);
+      }
+    },
+    updateCurrentCharset(aDocument) {
+      let currentCharset = aDocument.defaultView.gBrowser.selectedBrowser.characterSet;
+      currentCharset = CharsetMenu.foldCharset(currentCharset);
+
+      let pinnedContainer = aDocument.getElementById("PanelUI-characterEncodingView-pinned");
+      let charsetContainer = aDocument.getElementById("PanelUI-characterEncodingView-charsets");
+      let elements = [...(pinnedContainer.childNodes), ...(charsetContainer.childNodes)];
+
+      this._updateElements(elements, currentCharset);
+    },
+    updateCurrentDetector(aDocument) {
+      let detectorContainer = aDocument.getElementById("PanelUI-characterEncodingView-autodetect");
+      let currentDetector;
+      try {
+        currentDetector = Services.prefs.getComplexValue(
+          "intl.charset.detector", Ci.nsIPrefLocalizedString).data;
+      } catch (e) {}
+
+      this._updateElements(detectorContainer.childNodes, currentDetector);
+    },
+    _updateElements(aElements, aCurrentItem) {
+      if (!aElements.length) {
+        return;
+      }
+      let disabled = this.maybeDisableMenu(aElements[0].ownerDocument);
+      for (let elem of aElements) {
+        if (disabled) {
+          elem.setAttribute("disabled", "true");
+        } else {
+          elem.removeAttribute("disabled");
+        }
+        if (elem.value.toLowerCase() == aCurrentItem.toLowerCase()) {
+          elem.setAttribute("checked", "true");
+        } else {
+          elem.removeAttribute("checked");
+        }
+      }
+    },
+    onViewShowing(aEvent) {
+      let document = aEvent.target.ownerDocument;
+
+      let autoDetectLabelId = "PanelUI-characterEncodingView-autodetect-label";
+      let autoDetectLabel = document.getElementById(autoDetectLabelId);
+      if (!autoDetectLabel.hasAttribute("value")) {
+        let label = CharsetBundle.GetStringFromName("charsetMenuAutodet");
+        autoDetectLabel.setAttribute("value", label);
+        this.populateList(document,
+                          "PanelUI-characterEncodingView-pinned",
+                          "pinnedCharsets");
+        this.populateList(document,
+                          "PanelUI-characterEncodingView-charsets",
+                          "otherCharsets");
+        this.populateList(document,
+                          "PanelUI-characterEncodingView-autodetect",
+                          "detectors");
+      }
+      this.updateCurrentDetector(document);
+      this.updateCurrentCharset(document);
+    },
+    onCommand(aEvent) {
+      let node = aEvent.target;
+      if (!node.hasAttribute || !node.section) {
+        return;
+      }
+
+      let window = node.ownerGlobal;
+      let section = node.section;
+      let value = node.value;
+
+      // The behavior as implemented here is directly based off of the
+      // `MultiplexHandler()` method in browser.js.
+      if (section != "detectors") {
+        window.BrowserSetForcedCharacterSet(value);
+      } else {
+        // Set the detector pref.
+        try {
+          let str = Cc["@mozilla.org/supports-string;1"]
+                      .createInstance(Ci.nsISupportsString);
+          str.data = value;
+          Services.prefs.setComplexValue("intl.charset.detector", Ci.nsISupportsString, str);
+        } catch (e) {
+          Cu.reportError("Failed to set the intl.charset.detector preference.");
+        }
+        // Prepare a browser page reload with a changed charset.
+        window.BrowserCharsetReload();
+      }
+    },
+    onCreated(aNode) {
+      const kPanelId = "PanelUI-popup";
+      let document = aNode.ownerDocument;
+
+      let updateButton = () => {
+        if (this.maybeDisableMenu(document))
+          aNode.setAttribute("disabled", "true");
+        else
+          aNode.removeAttribute("disabled");
+      };
+
+      if (this.currentArea == CustomizableUI.AREA_PANEL) {
+        let panel = document.getElementById(kPanelId);
+        panel.addEventListener("popupshowing", updateButton);
+      }
+
+      let listener = {
+        onWidgetAdded: (aWidgetId, aArea) => {
+          if (aWidgetId != this.id)
+            return;
+          if (aArea == CustomizableUI.AREA_PANEL) {
+            let panel = document.getElementById(kPanelId);
+            panel.addEventListener("popupshowing", updateButton);
+          }
+        },
+        onWidgetRemoved: (aWidgetId, aPrevArea) => {
+          if (aWidgetId != this.id)
+            return;
+          aNode.removeAttribute("disabled");
+          if (aPrevArea == CustomizableUI.AREA_PANEL) {
+            let panel = document.getElementById(kPanelId);
+            panel.removeEventListener("popupshowing", updateButton);
+          }
+        },
+        onWidgetInstanceRemoved: (aWidgetId, aDoc) => {
+          if (aWidgetId != this.id || aDoc != document)
+            return;
+
+          CustomizableUI.removeListener(listener);
+          let panel = aDoc.getElementById(kPanelId);
+          panel.removeEventListener("popupshowing", updateButton);
+        }
+      };
+      CustomizableUI.addListener(listener);
+      if (!this.charsetInfo) {
+        this.charsetInfo = CharsetMenu.getData();
+      }
+    }
+  }, {
+    id: "email-link-button",
+    tooltiptext: "email-link-button.tooltiptext3",
+    onCommand(aEvent) {
+      let win = aEvent.view;
+      win.MailIntegration.sendLinkForBrowser(win.gBrowser.selectedBrowser)
+    }
+  }, {
+    id: "containers-panelmenu",
+    type: "view",
+    viewId: "PanelUI-containers",
+    hasObserver: false,
+    onCreated(aNode) {
+      let doc = aNode.ownerDocument;
+      let win = doc.defaultView;
+      let items = doc.getElementById("PanelUI-containersItems");
+
+      let onItemCommand = function(aEvent) {
+        let item = aEvent.target;
+        if (item.hasAttribute("usercontextid")) {
+          let userContextId = parseInt(item.getAttribute("usercontextid"));
+          win.openUILinkIn(win.BROWSER_NEW_TAB_URL, "tab", {userContextId});
+        }
+      };
+      items.addEventListener("command", onItemCommand);
+
+      if (PrivateBrowsingUtils.isWindowPrivate(win)) {
+        aNode.setAttribute("disabled", "true");
+      }
+
+      this.updateVisibility(aNode);
+
+      if (!this.hasObserver) {
+        Services.prefs.addObserver("privacy.userContext.enabled", this, true);
+        this.hasObserver = true;
+      }
+    },
+    onViewShowing(aEvent) {
+      let doc = aEvent.target.ownerDocument;
+
+      let items = doc.getElementById("PanelUI-containersItems");
+
+      while (items.firstChild) {
+        items.firstChild.remove();
+      }
+
+      let fragment = doc.createDocumentFragment();
+      let bundle = doc.getElementById("bundle_browser");
+
+      ContextualIdentityService.getIdentities().forEach(identity => {
+        let label = ContextualIdentityService.getUserContextLabel(identity.userContextId);
+
+        let item = doc.createElementNS(kNSXUL, "toolbarbutton");
+        item.setAttribute("label", label);
+        item.setAttribute("usercontextid", identity.userContextId);
+        item.setAttribute("class", "subviewbutton");
+        item.setAttribute("data-identity-color", identity.color);
+        item.setAttribute("data-identity-icon", identity.icon);
+
+        fragment.appendChild(item);
+      });
+
+      fragment.appendChild(doc.createElementNS(kNSXUL, "menuseparator"));
+
+      let item = doc.createElementNS(kNSXUL, "toolbarbutton");
+      item.setAttribute("label", bundle.getString("userContext.aboutPage.label"));
+      item.setAttribute("command", "Browser:OpenAboutContainers");
+      item.setAttribute("class", "subviewbutton");
+      fragment.appendChild(item);
+
+      items.appendChild(fragment);
+    },
+
+    updateVisibility(aNode) {
+      aNode.hidden = !Services.prefs.getBoolPref("privacy.userContext.enabled");
+    },
+
+    observe(aSubject, aTopic, aData) {
+      let {instances} = CustomizableUI.getWidget("containers-panelmenu");
+      for (let {node} of instances) {
+	if (node) {
+	  this.updateVisibility(node);
+	}
+      }
+    },
+
+    QueryInterface: XPCOMUtils.generateQI([
+      Ci.nsISupportsWeakReference,
+      Ci.nsIObserver
+    ]),
+  }];
+
+let preferencesButton = {
+  id: "preferences-button",
+  defaultArea: CustomizableUI.AREA_PANEL,
+  onCommand(aEvent) {
+    let win = aEvent.target.ownerGlobal;
+    win.openPreferences();
+  }
+};
+#ifdef XP_MACOSX
+preferencesButton.tooltiptext = "preferences-button.tooltiptext.withshortcut";
+preferencesButton.shortcutId = "key_preferencesCmdMac";
+#else
+preferencesButton.tooltiptext = "preferences-button.tooltiptext2";
+#endif
+CustomizableWidgets.push(preferencesButton);
+
+if (Services.prefs.getBoolPref("privacy.panicButton.enabled")) {
+  CustomizableWidgets.push({
+    id: "panic-button",
+    type: "view",
+    viewId: "PanelUI-panicView",
+    _sanitizer: null,
+    _ensureSanitizer() {
+      if (!this.sanitizer) {
+        let scope = {};
+        Services.scriptloader.loadSubScript("chrome://browser/content/sanitize.js",
+                                            scope);
+        this._Sanitizer = scope.Sanitizer;
+        this._sanitizer = new scope.Sanitizer();
+        this._sanitizer.ignoreTimespan = false;
+      }
+    },
+    _getSanitizeRange(aDocument) {
+      let group = aDocument.getElementById("PanelUI-panic-timeSpan");
+      return this._Sanitizer.getClearRange(+group.value);
+    },
+    forgetButtonCalled(aEvent) {
+      let doc = aEvent.target.ownerDocument;
+      this._ensureSanitizer();
+      this._sanitizer.range = this._getSanitizeRange(doc);
+      let group = doc.getElementById("PanelUI-panic-timeSpan");
+      BrowserUITelemetry.countPanicEvent(group.selectedItem.id);
+      group.selectedItem = doc.getElementById("PanelUI-panic-5min");
+      let itemsToClear = [
+        "cookies", "history", "openWindows", "formdata", "sessions", "cache", "downloads", "offlineApps"
+      ];
+      let newWindowPrivateState = PrivateBrowsingUtils.isWindowPrivate(doc.defaultView) ?
+                                  "private" : "non-private";
+      this._sanitizer.items.openWindows.privateStateForNewWindow = newWindowPrivateState;
+      let promise = this._sanitizer.sanitize(itemsToClear);
+      promise.then(function() {
+        let otherWindow = Services.wm.getMostRecentWindow("navigator:browser");
+        if (otherWindow.closed) {
+          Cu.reportError("Got a closed window!");
+        }
+        if (otherWindow.PanicButtonNotifier) {
+          otherWindow.PanicButtonNotifier.notify();
+        } else {
+          otherWindow.PanicButtonNotifierShouldNotify = true;
+        }
+      });
+    },
+    handleEvent(aEvent) {
+      switch (aEvent.type) {
+        case "command":
+          this.forgetButtonCalled(aEvent);
+          break;
+      }
+    },
+    onViewShowing(aEvent) {
+      let forgetButton = aEvent.target.querySelector("#PanelUI-panic-view-button");
+      forgetButton.addEventListener("command", this);
+    },
+    onViewHiding(aEvent) {
+      let forgetButton = aEvent.target.querySelector("#PanelUI-panic-view-button");
+      forgetButton.removeEventListener("command", this);
+    },
+  });
+}
+
+#ifdef E10S_TESTING_ONLY
+if (Services.appinfo.browserTabsRemoteAutostart) {
+  CustomizableWidgets.push({
+    id: "e10s-button",
+    defaultArea: CustomizableUI.AREA_PANEL,
+    onBuild(aDocument) {
+      let node = aDocument.createElementNS(kNSXUL, "toolbarbutton");
+      node.setAttribute("label", CustomizableUI.getLocalizedProperty(this, "label"));
+      node.setAttribute("tooltiptext", CustomizableUI.getLocalizedProperty(this, "tooltiptext"));
+    },
+    onCommand(aEvent) {
+      let win = aEvent.view;
+      win.OpenBrowserWindow({remote: false});
+    },
+  });
+}
+#endif
diff --git a/application/basilisk/components/customizableui/CustomizeMode.jsm b/application/basilisk/components/customizableui/CustomizeMode.jsm
new file mode 100644
index 000000000..b756ab8a7
--- /dev/null
+++ b/application/basilisk/components/customizableui/CustomizeMode.jsm
@@ -0,0 +1,2350 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+this.EXPORTED_SYMBOLS = ["CustomizeMode"];
+
+const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;
+
+const kPrefCustomizationDebug = "browser.uiCustomization.debug";
+const kPrefCustomizationAnimation = "browser.uiCustomization.disableAnimation";
+const kPaletteId = "customization-palette";
+const kDragDataTypePrefix = "text/toolbarwrapper-id/";
+const kPlaceholderClass = "panel-customization-placeholder";
+const kSkipSourceNodePref = "browser.uiCustomization.skipSourceNodeCheck";
+const kToolbarVisibilityBtn = "customization-toolbar-visibility-button";
+const kDrawInTitlebarPref = "browser.tabs.drawInTitlebar";
+const kMaxTransitionDurationMs = 2000;
+
+const kPanelItemContextMenu = "customizationPanelItemContextMenu";
+const kPaletteItemContextMenu = "customizationPaletteItemContextMenu";
+
+Cu.import("resource://gre/modules/Services.jsm");
+Cu.import("resource:///modules/CustomizableUI.jsm");
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+Cu.import("resource://gre/modules/Task.jsm");
+Cu.import("resource://gre/modules/Promise.jsm");
+Cu.import("resource://gre/modules/AddonManager.jsm");
+
+XPCOMUtils.defineLazyModuleGetter(this, "DragPositionManager",
+                                  "resource:///modules/DragPositionManager.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "BrowserUITelemetry",
+                                  "resource:///modules/BrowserUITelemetry.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "LightweightThemeManager",
+                                  "resource://gre/modules/LightweightThemeManager.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "SessionStore",
+                                  "resource:///modules/sessionstore/SessionStore.jsm");
+
+let gDebug;
+XPCOMUtils.defineLazyGetter(this, "log", () => {
+  let scope = {};
+  Cu.import("resource://gre/modules/Console.jsm", scope);
+  try {
+    gDebug = Services.prefs.getBoolPref(kPrefCustomizationDebug);
+  } catch (ex) {}
+  let consoleOptions = {
+    maxLogLevel: gDebug ? "all" : "log",
+    prefix: "CustomizeMode",
+  };
+  return new scope.ConsoleAPI(consoleOptions);
+});
+
+var gDisableAnimation = null;
+
+var gDraggingInToolbars;
+
+var gTab;
+
+function closeGlobalTab() {
+  let win = gTab.ownerGlobal;
+  if (win.gBrowser.browsers.length == 1) {
+    win.BrowserOpenTab();
+  }
+  win.gBrowser.removeTab(gTab);
+  gTab = null;
+}
+
+function unregisterGlobalTab() {
+  gTab.removeEventListener("TabClose", unregisterGlobalTab);
+  gTab.ownerGlobal.removeEventListener("unload", unregisterGlobalTab);
+  gTab.removeAttribute("customizemode");
+  gTab = null;
+}
+
+function CustomizeMode(aWindow) {
+  if (gDisableAnimation === null) {
+    gDisableAnimation = Services.prefs.getPrefType(kPrefCustomizationAnimation) == Ci.nsIPrefBranch.PREF_BOOL &&
+                        Services.prefs.getBoolPref(kPrefCustomizationAnimation);
+  }
+  this.window = aWindow;
+  this.document = aWindow.document;
+  this.browser = aWindow.gBrowser;
+  this.areas = new Set();
+
+  // There are two palettes - there's the palette that can be overlayed with
+  // toolbar items in browser.xul. This is invisible, and never seen by the
+  // user. Then there's the visible palette, which gets populated and displayed
+  // to the user when in customizing mode.
+  this.visiblePalette = this.document.getElementById(kPaletteId);
+  this.paletteEmptyNotice = this.document.getElementById("customization-empty");
+  this.tipPanel = this.document.getElementById("customization-tipPanel");
+  if (Services.prefs.getCharPref("general.skins.selectedSkin") != "classic/1.0") {
+    let lwthemeButton = this.document.getElementById("customization-lwtheme-button");
+    lwthemeButton.setAttribute("hidden", "true");
+  }
+#ifdef CAN_DRAW_IN_TITLEBAR
+  this._updateTitlebarButton();
+  Services.prefs.addObserver(kDrawInTitlebarPref, this, false);
+#endif
+  this.window.addEventListener("unload", this);
+}
+
+CustomizeMode.prototype = {
+  _changed: false,
+  _transitioning: false,
+  window: null,
+  document: null,
+  // areas is used to cache the customizable areas when in customization mode.
+  areas: null,
+  // When in customizing mode, we swap out the reference to the invisible
+  // palette in gNavToolbox.palette for our visiblePalette. This way, for the
+  // customizing browser window, when widgets are removed from customizable
+  // areas and added to the palette, they're added to the visible palette.
+  // _stowedPalette is a reference to the old invisible palette so we can
+  // restore gNavToolbox.palette to its original state after exiting
+  // customization mode.
+  _stowedPalette: null,
+  _dragOverItem: null,
+  _customizing: false,
+  _skipSourceNodeCheck: null,
+  _mainViewContext: null,
+
+  get panelUIContents() {
+    return this.document.getElementById("PanelUI-contents");
+  },
+
+  get _handler() {
+    return this.window.CustomizationHandler;
+  },
+
+  uninit() {
+#ifdef CAN_DRAW_IN_TITLEBAR
+    Services.prefs.removeObserver(kDrawInTitlebarPref, this);
+#endif
+  },
+
+  toggle() {
+    if (this._handler.isEnteringCustomizeMode || this._handler.isExitingCustomizeMode) {
+      this._wantToBeInCustomizeMode = !this._wantToBeInCustomizeMode;
+      return;
+    }
+    if (this._customizing) {
+      this.exit();
+    } else {
+      this.enter();
+    }
+  },
+
+  _updateLWThemeButtonIcon() {
+    let lwthemeButton = this.document.getElementById("customization-lwtheme-button");
+    let lwthemeIcon = this.document.getAnonymousElementByAttribute(lwthemeButton,
+                        "class", "button-icon");
+    lwthemeIcon.style.backgroundImage = LightweightThemeManager.currentTheme ?
+      "url(" + LightweightThemeManager.currentTheme.iconURL + ")" : "";
+  },
+
+  setTab(aTab) {
+    if (gTab == aTab) {
+      return;
+    }
+
+    if (gTab) {
+      closeGlobalTab();
+    }
+
+    gTab = aTab;
+
+    gTab.setAttribute("customizemode", "true");
+    SessionStore.persistTabAttribute("customizemode");
+
+    gTab.linkedBrowser.stop();
+
+    let win = gTab.ownerGlobal;
+
+    win.gBrowser.setTabTitle(gTab);
+    win.gBrowser.setIcon(gTab,
+                         "chrome://browser/skin/customizableui/customizeFavicon.ico");
+
+    gTab.addEventListener("TabClose", unregisterGlobalTab);
+    win.addEventListener("unload", unregisterGlobalTab);
+
+    if (gTab.selected) {
+      win.gCustomizeMode.enter();
+    }
+  },
+
+  enter() {
+    this._wantToBeInCustomizeMode = true;
+
+    if (this._customizing || this._handler.isEnteringCustomizeMode) {
+      return;
+    }
+
+    // Exiting; want to re-enter once we've done that.
+    if (this._handler.isExitingCustomizeMode) {
+      log.debug("Attempted to enter while we're in the middle of exiting. " +
+                "We'll exit after we've entered");
+      return;
+    }
+
+    if (!gTab) {
+      this.setTab(this.browser.loadOneTab("about:blank",
+                                          { inBackground: false,
+                                            forceNotRemote: true,
+                                            skipAnimation: true }));
+      return;
+    }
+    if (!gTab.selected) {
+      // This will force another .enter() to be called via the
+      // onlocationchange handler of the tabbrowser, so we return early.
+      gTab.ownerGlobal.gBrowser.selectedTab = gTab;
+      return;
+    }
+    gTab.ownerGlobal.focus();
+    if (gTab.ownerDocument != this.document) {
+      return;
+    }
+
+    let window = this.window;
+    let document = this.document;
+
+    this._handler.isEnteringCustomizeMode = true;
+
+    // Always disable the reset button at the start of customize mode, it'll be re-enabled
+    // if necessary when we finish entering:
+    let resetButton = this.document.getElementById("customization-reset-button");
+    resetButton.setAttribute("disabled", "true");
+
+    Task.spawn(function*() {
+      // We shouldn't start customize mode until after browser-delayed-startup has finished:
+      if (!this.window.gBrowserInit.delayedStartupFinished) {
+        yield new Promise(resolve => {
+          let delayedStartupObserver = aSubject => {
+            if (aSubject == this.window) {
+              Services.obs.removeObserver(delayedStartupObserver, "browser-delayed-startup-finished");
+              resolve();
+            }
+          };
+
+          Services.obs.addObserver(delayedStartupObserver, "browser-delayed-startup-finished", false);
+        });
+      }
+
+      let toolbarVisibilityBtn = document.getElementById(kToolbarVisibilityBtn);
+      let togglableToolbars = window.getTogglableToolbars();
+      if (togglableToolbars.length == 0) {
+        toolbarVisibilityBtn.setAttribute("hidden", "true");
+      } else {
+        toolbarVisibilityBtn.removeAttribute("hidden");
+      }
+
+      this.updateLWTStyling();
+
+      CustomizableUI.dispatchToolboxEvent("beforecustomization", {}, window);
+      CustomizableUI.notifyStartCustomizing(this.window);
+
+      // Add a keypress listener to the document so that we can quickly exit
+      // customization mode when pressing ESC.
+      document.addEventListener("keypress", this);
+
+      // Same goes for the menu button - if we're customizing, a click on the
+      // menu button means a quick exit from customization mode.
+      window.PanelUI.hide();
+      window.PanelUI.menuButton.addEventListener("command", this);
+      window.PanelUI.menuButton.open = true;
+      window.PanelUI.beginBatchUpdate();
+
+      // The menu panel is lazy, and registers itself when the popup shows. We
+      // need to force the menu panel to register itself, or else customization
+      // is really not going to work. We pass "true" to ensureReady to
+      // indicate that we're handling calling startBatchUpdate and
+      // endBatchUpdate.
+      if (!window.PanelUI.isReady) {
+        yield window.PanelUI.ensureReady(true);
+      }
+
+      // Hide the palette before starting the transition for increased perf.
+      this.visiblePalette.hidden = true;
+      this.visiblePalette.removeAttribute("showing");
+
+      // Disable the button-text fade-out mask
+      // during the transition for increased perf.
+      let panelContents = window.PanelUI.contents;
+      panelContents.setAttribute("customize-transitioning", "true");
+
+      // Move the mainView in the panel to the holder so that we can see it
+      // while customizing.
+      let mainView = window.PanelUI.mainView;
+      let panelHolder = document.getElementById("customization-panelHolder");
+      panelHolder.appendChild(mainView);
+
+      let customizeButton = document.getElementById("PanelUI-customize");
+      customizeButton.setAttribute("enterLabel", customizeButton.getAttribute("label"));
+      customizeButton.setAttribute("label", customizeButton.getAttribute("exitLabel"));
+      customizeButton.setAttribute("enterTooltiptext", customizeButton.getAttribute("tooltiptext"));
+      customizeButton.setAttribute("tooltiptext", customizeButton.getAttribute("exitTooltiptext"));
+
+      this._transitioning = true;
+
+      let customizer = document.getElementById("customization-container");
+      customizer.parentNode.selectedPanel = customizer;
+      customizer.hidden = false;
+
+      this._wrapToolbarItemSync(CustomizableUI.AREA_TABSTRIP);
+
+      let customizableToolbars = document.querySelectorAll("toolbar[customizable=true]:not([autohide=true]):not([collapsed=true])");
+      for (let toolbar of customizableToolbars)
+        toolbar.setAttribute("customizing", true);
+
+      yield this._doTransition(true);
+
+      Services.obs.addObserver(this, "lightweight-theme-window-updated", false);
+
+      // Let everybody in this window know that we're about to customize.
+      CustomizableUI.dispatchToolboxEvent("customizationstarting", {}, window);
+
+      this._mainViewContext = mainView.getAttribute("context");
+      if (this._mainViewContext) {
+        mainView.removeAttribute("context");
+      }
+
+      this._showPanelCustomizationPlaceholders();
+
+      yield this._wrapToolbarItems();
+      this.populatePalette();
+
+      this._addDragHandlers(this.visiblePalette);
+
+      window.gNavToolbox.addEventListener("toolbarvisibilitychange", this);
+
+      document.getElementById("PanelUI-help").setAttribute("disabled", true);
+      document.getElementById("PanelUI-quit").setAttribute("disabled", true);
+
+      this._updateResetButton();
+      this._updateUndoResetButton();
+
+      this._skipSourceNodeCheck = Services.prefs.getPrefType(kSkipSourceNodePref) == Ci.nsIPrefBranch.PREF_BOOL &&
+                                  Services.prefs.getBoolPref(kSkipSourceNodePref);
+
+      CustomizableUI.addListener(this);
+      window.PanelUI.endBatchUpdate();
+      this._customizing = true;
+      this._transitioning = false;
+
+      // Show the palette now that the transition has finished.
+      this.visiblePalette.hidden = false;
+      window.setTimeout(() => {
+        // Force layout reflow to ensure the animation runs,
+        // and make it async so it doesn't affect the timing.
+        this.visiblePalette.clientTop;
+        this.visiblePalette.setAttribute("showing", "true");
+      }, 0);
+      this._updateEmptyPaletteNotice();
+
+      this._updateLWThemeButtonIcon();
+      this.maybeShowTip(panelHolder);
+
+      this._handler.isEnteringCustomizeMode = false;
+      panelContents.removeAttribute("customize-transitioning");
+
+      CustomizableUI.dispatchToolboxEvent("customizationready", {}, window);
+      this._enableOutlinesTimeout = window.setTimeout(() => {
+        this.document.getElementById("nav-bar").setAttribute("showoutline", "true");
+        this.panelUIContents.setAttribute("showoutline", "true");
+        delete this._enableOutlinesTimeout;
+      }, 0);
+
+      if (!this._wantToBeInCustomizeMode) {
+        this.exit();
+      }
+    }.bind(this)).then(null, function(e) {
+      log.error("Error entering customize mode", e);
+      // We should ensure this has been called, and calling it again doesn't hurt:
+      window.PanelUI.endBatchUpdate();
+      this._handler.isEnteringCustomizeMode = false;
+      // Exit customize mode to ensure proper clean-up when entering failed.
+      this.exit();
+    }.bind(this));
+  },
+
+  exit() {
+    this._wantToBeInCustomizeMode = false;
+
+    if (!this._customizing || this._handler.isExitingCustomizeMode) {
+      return;
+    }
+
+    // Entering; want to exit once we've done that.
+    if (this._handler.isEnteringCustomizeMode) {
+      log.debug("Attempted to exit while we're in the middle of entering. " +
+                "We'll exit after we've entered");
+      return;
+    }
+
+    if (this.resetting) {
+      log.debug("Attempted to exit while we're resetting. " +
+                "We'll exit after resetting has finished.");
+      return;
+    }
+
+    this.hideTip();
+
+    this._handler.isExitingCustomizeMode = true;
+
+    if (this._enableOutlinesTimeout) {
+      this.window.clearTimeout(this._enableOutlinesTimeout);
+    } else {
+      this.document.getElementById("nav-bar").removeAttribute("showoutline");
+      this.panelUIContents.removeAttribute("showoutline");
+    }
+
+    this._removeExtraToolbarsIfEmpty();
+
+    CustomizableUI.removeListener(this);
+
+    this.document.removeEventListener("keypress", this);
+    this.window.PanelUI.menuButton.removeEventListener("command", this);
+    this.window.PanelUI.menuButton.open = false;
+
+    this.window.PanelUI.beginBatchUpdate();
+
+    this._removePanelCustomizationPlaceholders();
+
+    let window = this.window;
+    let document = this.document;
+
+    // Hide the palette before starting the transition for increased perf.
+    this.visiblePalette.hidden = true;
+    this.visiblePalette.removeAttribute("showing");
+    this.paletteEmptyNotice.hidden = true;
+
+    // Disable the button-text fade-out mask
+    // during the transition for increased perf.
+    let panelContents = window.PanelUI.contents;
+    panelContents.setAttribute("customize-transitioning", "true");
+
+    // Disable the reset and undo reset buttons while transitioning:
+    let resetButton = this.document.getElementById("customization-reset-button");
+    let undoResetButton = this.document.getElementById("customization-undo-reset-button");
+    undoResetButton.hidden = resetButton.disabled = true;
+
+    this._transitioning = true;
+
+    Task.spawn(function*() {
+      yield this.depopulatePalette();
+
+      yield this._doTransition(false);
+      this.removeLWTStyling();
+
+      Services.obs.removeObserver(this, "lightweight-theme-window-updated");
+
+      if (this.browser.selectedTab == gTab) {
+        if (gTab.linkedBrowser.currentURI.spec == "about:blank") {
+          closeGlobalTab();
+        } else {
+          unregisterGlobalTab();
+        }
+      }
+      let browser = document.getElementById("browser");
+      browser.parentNode.selectedPanel = browser;
+      let customizer = document.getElementById("customization-container");
+      customizer.hidden = true;
+
+      window.gNavToolbox.removeEventListener("toolbarvisibilitychange", this);
+
+      DragPositionManager.stop();
+      this._removeDragHandlers(this.visiblePalette);
+
+      yield this._unwrapToolbarItems();
+
+      if (this._changed) {
+        // XXXmconley: At first, it seems strange to also persist the old way with
+        //             currentset - but this might actually be useful for switching
+        //             to old builds. We might want to keep this around for a little
+        //             bit.
+        this.persistCurrentSets();
+      }
+
+      // And drop all area references.
+      this.areas.clear();
+
+      // Let everybody in this window know that we're starting to
+      // exit customization mode.
+      CustomizableUI.dispatchToolboxEvent("customizationending", {}, window);
+
+      window.PanelUI.setMainView(window.PanelUI.mainView);
+      window.PanelUI.menuButton.disabled = false;
+
+      let customizeButton = document.getElementById("PanelUI-customize");
+      customizeButton.setAttribute("exitLabel", customizeButton.getAttribute("label"));
+      customizeButton.setAttribute("label", customizeButton.getAttribute("enterLabel"));
+      customizeButton.setAttribute("exitTooltiptext", customizeButton.getAttribute("tooltiptext"));
+      customizeButton.setAttribute("tooltiptext", customizeButton.getAttribute("enterTooltiptext"));
+
+      // We have to use setAttribute/removeAttribute here instead of the
+      // property because the XBL property will be set later, and right
+      // now we'd be setting an expando, which breaks the XBL property.
+      document.getElementById("PanelUI-help").removeAttribute("disabled");
+      document.getElementById("PanelUI-quit").removeAttribute("disabled");
+
+      panelContents.removeAttribute("customize-transitioning");
+
+      // We need to set this._customizing to false before removing the tab
+      // or the TabSelect event handler will think that we are exiting
+      // customization mode for a second time.
+      this._customizing = false;
+
+      let mainView = window.PanelUI.mainView;
+      if (this._mainViewContext) {
+        mainView.setAttribute("context", this._mainViewContext);
+      }
+
+      let customizableToolbars = document.querySelectorAll("toolbar[customizable=true]:not([autohide=true])");
+      for (let toolbar of customizableToolbars)
+        toolbar.removeAttribute("customizing");
+
+      this.window.PanelUI.endBatchUpdate();
+      delete this._lastLightweightTheme;
+      this._changed = false;
+      this._transitioning = false;
+      this._handler.isExitingCustomizeMode = false;
+      CustomizableUI.dispatchToolboxEvent("aftercustomization", {}, window);
+      CustomizableUI.notifyEndCustomizing(window);
+
+      if (this._wantToBeInCustomizeMode) {
+        this.enter();
+      }
+    }.bind(this)).then(null, function(e) {
+      log.error("Error exiting customize mode", e);
+      // We should ensure this has been called, and calling it again doesn't hurt:
+      window.PanelUI.endBatchUpdate();
+      this._handler.isExitingCustomizeMode = false;
+    }.bind(this));
+  },
+
+  /**
+   * The customize mode transition has 4 phases when entering:
+   * 1) Pre-customization mode
+   *    This is the starting phase of the browser.
+   * 2) LWT swapping
+   *    This is where we swap some of the lightweight theme styles in order
+   *    to make them work in customize mode. We set/unset a customization-
+   *    lwtheme attribute iff we're using a lightweight theme.
+   * 3) customize-entering
+   *    This phase is a transition, optimized for smoothness.
+   * 4) customize-entered
+   *    After the transition completes, this phase draws all of the
+   *    expensive detail that isn't necessary during the second phase.
+   *
+   * Exiting customization mode has a similar set of phases, but in reverse
+   * order - customize-entered, customize-exiting, remove LWT swapping,
+   * pre-customization mode.
+   *
+   * When in the customize-entering, customize-entered, or customize-exiting
+   * phases, there is a "customizing" attribute set on the main-window to simplify
+   * excluding certain styles while in any phase of customize mode.
+   */
+  _doTransition(aEntering) {
+    let deck = this.document.getElementById("content-deck");
+    let customizeTransitionEndPromise = new Promise(resolve => {
+      let customizeTransitionEnd = (aEvent) => {
+        if (aEvent != "timedout" &&
+            (aEvent.originalTarget != deck || aEvent.propertyName != "margin-left")) {
+          return;
+        }
+        this.window.clearTimeout(catchAllTimeout);
+        // We request an animation frame to do the final stage of the transition
+        // to improve perceived performance. (bug 962677)
+        this.window.requestAnimationFrame(() => {
+          deck.removeEventListener("transitionend", customizeTransitionEnd);
+
+          if (!aEntering) {
+            this.document.documentElement.removeAttribute("customize-exiting");
+            this.document.documentElement.removeAttribute("customizing");
+          } else {
+            this.document.documentElement.setAttribute("customize-entered", true);
+            this.document.documentElement.removeAttribute("customize-entering");
+          }
+          CustomizableUI.dispatchToolboxEvent("customization-transitionend", aEntering, this.window);
+
+          resolve();
+        });
+      };
+      deck.addEventListener("transitionend", customizeTransitionEnd);
+      let catchAll = () => customizeTransitionEnd("timedout");
+      let catchAllTimeout = this.window.setTimeout(catchAll, kMaxTransitionDurationMs);
+    });
+
+    if (gDisableAnimation) {
+      this.document.getElementById("tab-view-deck").setAttribute("fastcustomizeanimation", true);
+    }
+
+    if (aEntering) {
+      this.document.documentElement.setAttribute("customizing", true);
+      this.document.documentElement.setAttribute("customize-entering", true);
+    } else {
+      this.document.documentElement.setAttribute("customize-exiting", true);
+      this.document.documentElement.removeAttribute("customize-entered");
+    }
+
+    return customizeTransitionEndPromise;
+  },
+
+  updateLWTStyling(aData) {
+    let docElement = this.document.documentElement;
+    if (!aData) {
+      let lwt = docElement._lightweightTheme;
+      aData = lwt.getData();
+    }
+    let headerURL = aData && aData.headerURL;
+    if (!headerURL) {
+      this.removeLWTStyling();
+      return;
+    }
+
+    let deck = this.document.getElementById("tab-view-deck");
+    let headerImageRef = this._getHeaderImageRef(aData);
+    docElement.setAttribute("customization-lwtheme", "true");
+
+    let toolboxRect = this.window.gNavToolbox.getBoundingClientRect();
+    let height = toolboxRect.bottom;
+
+#ifdef XP_MACOSX
+    let drawingInTitlebar = !docElement.hasAttribute("drawtitle");
+    let titlebar = this.document.getElementById("titlebar");
+    if (drawingInTitlebar) {
+      titlebar.style.backgroundImage = headerImageRef;
+    } else {
+      titlebar.style.removeProperty("background-image");
+    }
+#endif
+
+    let limitedBG = "-moz-image-rect(" + headerImageRef + ", 0, 100%, " +
+                    height + ", 0)";
+
+    let ridgeStart = height - 1;
+    let ridgeCenter = (ridgeStart + 1) + "px";
+    let ridgeEnd = (ridgeStart + 2) + "px";
+    ridgeStart = ridgeStart + "px";
+
+    let ridge = "linear-gradient(to bottom, " +
+                                 "transparent " + ridgeStart +
+                                 ", rgba(0,0,0,0.25) " + ridgeStart +
+                                 ", rgba(0,0,0,0.25) " + ridgeCenter +
+                                 ", rgba(255,255,255,0.5) " + ridgeCenter +
+                                 ", rgba(255,255,255,0.5) " + ridgeEnd + ", " +
+                                 "transparent " + ridgeEnd + ")";
+    deck.style.backgroundImage = ridge + ", " + limitedBG;
+
+    /* Remove the background styles from the <window> so we can style it instead. */
+    docElement.style.removeProperty("background-image");
+    docElement.style.removeProperty("background-color");
+  },
+
+  removeLWTStyling() {
+#ifdef XP_MACOSX
+    let affectedNodes = ["tab-view-deck", "titlebar"];
+#else
+    let affectedNodes = ["tab-view-deck"];
+#endif
+    for (let id of affectedNodes) {
+      let node = this.document.getElementById(id);
+      node.style.removeProperty("background-image");
+    }
+    let docElement = this.document.documentElement;
+    docElement.removeAttribute("customization-lwtheme");
+    let data = docElement._lightweightTheme.getData();
+    if (data && data.headerURL) {
+      docElement.style.backgroundImage = this._getHeaderImageRef(data);
+      docElement.style.backgroundColor = data.accentcolor || "white";
+    }
+  },
+
+  _getHeaderImageRef(aData) {
+    return "url(\"" + aData.headerURL.replace(/"/g, '\\"') + "\")";
+  },
+
+  maybeShowTip(aAnchor) {
+    let shown = false;
+    const kShownPref = "browser.customizemode.tip0.shown";
+    try {
+      shown = Services.prefs.getBoolPref(kShownPref);
+    } catch (ex) {}
+    if (shown)
+      return;
+
+    let anchorNode = aAnchor || this.document.getElementById("customization-panelHolder");
+    let messageNode = this.tipPanel.querySelector(".customization-tipPanel-contentMessage");
+    if (!messageNode.childElementCount) {
+      // Put the tip contents in the popup.
+      let bundle = this.document.getElementById("bundle_browser");
+      const kLabelClass = "customization-tipPanel-link";
+      messageNode.innerHTML = bundle.getFormattedString("customizeTips.tip0", [
+        "<label class=\"customization-tipPanel-em\" value=\"" +
+          bundle.getString("customizeTips.tip0.hint") + "\"/>",
+        this.document.getElementById("bundle_brand").getString("brandShortName"),
+        "<label class=\"" + kLabelClass + " text-link\" value=\"" +
+        bundle.getString("customizeTips.tip0.learnMore") + "\"/>"
+      ]);
+
+      messageNode.querySelector("." + kLabelClass).addEventListener("click", () => {
+        let url = Services.urlFormatter.formatURLPref("browser.customizemode.tip0.learnMoreUrl");
+        let browser = this.browser;
+        browser.selectedTab = browser.addTab(url);
+        this.hideTip();
+      });
+    }
+
+    this.tipPanel.hidden = false;
+    this.tipPanel.openPopup(anchorNode);
+    Services.prefs.setBoolPref(kShownPref, true);
+  },
+
+  hideTip() {
+    this.tipPanel.hidePopup();
+  },
+
+  _getCustomizableChildForNode(aNode) {
+    // NB: adjusted from _getCustomizableParent to keep that method fast
+    // (it's used during drags), and avoid multiple DOM loops
+    let areas = CustomizableUI.areas;
+    // Caching this length is important because otherwise we'll also iterate
+    // over items we add to the end from within the loop.
+    let numberOfAreas = areas.length;
+    for (let i = 0; i < numberOfAreas; i++) {
+      let area = areas[i];
+      let areaNode = aNode.ownerDocument.getElementById(area);
+      let customizationTarget = areaNode && areaNode.customizationTarget;
+      if (customizationTarget && customizationTarget != areaNode) {
+        areas.push(customizationTarget.id);
+      }
+      let overflowTarget = areaNode && areaNode.getAttribute("overflowtarget");
+      if (overflowTarget) {
+        areas.push(overflowTarget);
+      }
+    }
+    areas.push(kPaletteId);
+
+    while (aNode && aNode.parentNode) {
+      let parent = aNode.parentNode;
+      if (areas.indexOf(parent.id) != -1) {
+        return aNode;
+      }
+      aNode = parent;
+    }
+    return null;
+  },
+
+  addToToolbar(aNode) {
+    aNode = this._getCustomizableChildForNode(aNode);
+    if (aNode.localName == "toolbarpaletteitem" && aNode.firstChild) {
+      aNode = aNode.firstChild;
+    }
+    CustomizableUI.addWidgetToArea(aNode.id, CustomizableUI.AREA_NAVBAR);
+    if (!this._customizing) {
+      CustomizableUI.dispatchToolboxEvent("customizationchange");
+    }
+  },
+
+  addToPanel(aNode) {
+    aNode = this._getCustomizableChildForNode(aNode);
+    if (aNode.localName == "toolbarpaletteitem" && aNode.firstChild) {
+      aNode = aNode.firstChild;
+    }
+    CustomizableUI.addWidgetToArea(aNode.id, CustomizableUI.AREA_PANEL);
+    if (!this._customizing) {
+      CustomizableUI.dispatchToolboxEvent("customizationchange");
+    }
+  },
+
+  removeFromArea(aNode) {
+    aNode = this._getCustomizableChildForNode(aNode);
+    if (aNode.localName == "toolbarpaletteitem" && aNode.firstChild) {
+      aNode = aNode.firstChild;
+    }
+    CustomizableUI.removeWidgetFromArea(aNode.id);
+    if (!this._customizing) {
+      CustomizableUI.dispatchToolboxEvent("customizationchange");
+    }
+  },
+
+  populatePalette() {
+    let fragment = this.document.createDocumentFragment();
+    let toolboxPalette = this.window.gNavToolbox.palette;
+
+    try {
+      let unusedWidgets = CustomizableUI.getUnusedWidgets(toolboxPalette);
+      for (let widget of unusedWidgets) {
+        let paletteItem = this.makePaletteItem(widget, "palette");
+        if (!paletteItem) {
+          continue;
+        }
+        fragment.appendChild(paletteItem);
+      }
+
+      this.visiblePalette.appendChild(fragment);
+      this._stowedPalette = this.window.gNavToolbox.palette;
+      this.window.gNavToolbox.palette = this.visiblePalette;
+    } catch (ex) {
+      log.error(ex);
+    }
+  },
+
+  // XXXunf Maybe this should use -moz-element instead of wrapping the node?
+  //       Would ensure no weird interactions/event handling from original node,
+  //       and makes it possible to put this in a lazy-loaded iframe/real tab
+  //       while still getting rid of the need for overlays.
+  makePaletteItem(aWidget, aPlace) {
+    let widgetNode = aWidget.forWindow(this.window).node;
+    if (!widgetNode) {
+      log.error("Widget with id " + aWidget.id + " does not return a valid node");
+      return null;
+    }
+    // Do not build a palette item for hidden widgets; there's not much to show.
+    if (widgetNode.hidden) {
+      return null;
+    }
+
+    let wrapper = this.createOrUpdateWrapper(widgetNode, aPlace);
+    wrapper.appendChild(widgetNode);
+    return wrapper;
+  },
+
+  depopulatePalette() {
+    return Task.spawn(function*() {
+      this.visiblePalette.hidden = true;
+      let paletteChild = this.visiblePalette.firstChild;
+      let nextChild;
+      while (paletteChild) {
+        nextChild = paletteChild.nextElementSibling;
+        let provider = CustomizableUI.getWidget(paletteChild.id).provider;
+        if (provider == CustomizableUI.PROVIDER_XUL) {
+          let unwrappedPaletteItem =
+            yield this.deferredUnwrapToolbarItem(paletteChild);
+          this._stowedPalette.appendChild(unwrappedPaletteItem);
+        } else if (provider == CustomizableUI.PROVIDER_API) {
+          // XXXunf Currently this doesn't destroy the (now unused) node. It would
+          //       be good to do so, but we need to keep strong refs to it in
+          //       CustomizableUI (can't iterate of WeakMaps), and there's the
+          //       question of what behavior wrappers should have if consumers
+          //       keep hold of them.
+          // widget.destroyInstance(widgetNode);
+        } else if (provider == CustomizableUI.PROVIDER_SPECIAL) {
+          this.visiblePalette.removeChild(paletteChild);
+        }
+
+        paletteChild = nextChild;
+      }
+      this.visiblePalette.hidden = false;
+      this.window.gNavToolbox.palette = this._stowedPalette;
+    }.bind(this)).then(null, log.error);
+  },
+
+  isCustomizableItem(aNode) {
+    return aNode.localName == "toolbarbutton" ||
+           aNode.localName == "toolbaritem" ||
+           aNode.localName == "toolbarseparator" ||
+           aNode.localName == "toolbarspring" ||
+           aNode.localName == "toolbarspacer";
+  },
+
+  isWrappedToolbarItem(aNode) {
+    return aNode.localName == "toolbarpaletteitem";
+  },
+
+  deferredWrapToolbarItem(aNode, aPlace) {
+    return new Promise(resolve => {
+      dispatchFunction(() => {
+        let wrapper = this.wrapToolbarItem(aNode, aPlace);
+        resolve(wrapper);
+      });
+    });
+  },
+
+  wrapToolbarItem(aNode, aPlace) {
+    if (!this.isCustomizableItem(aNode)) {
+      return aNode;
+    }
+    let wrapper = this.createOrUpdateWrapper(aNode, aPlace);
+
+    // It's possible that this toolbar node is "mid-flight" and doesn't have
+    // a parent, in which case we skip replacing it. This can happen if a
+    // toolbar item has been dragged into the palette. In that case, we tell
+    // CustomizableUI to remove the widget from its area before putting the
+    // widget in the palette - so the node will have no parent.
+    if (aNode.parentNode) {
+      aNode = aNode.parentNode.replaceChild(wrapper, aNode);
+    }
+    wrapper.appendChild(aNode);
+    return wrapper;
+  },
+
+  createOrUpdateWrapper(aNode, aPlace, aIsUpdate) {
+    let wrapper;
+    if (aIsUpdate && aNode.parentNode && aNode.parentNode.localName == "toolbarpaletteitem") {
+      wrapper = aNode.parentNode;
+      aPlace = wrapper.getAttribute("place");
+    } else {
+      wrapper = this.document.createElement("toolbarpaletteitem");
+      // "place" is used by toolkit to add the toolbarpaletteitem-palette
+      // binding to a toolbarpaletteitem, which gives it a label node for when
+      // it's sitting in the palette.
+      wrapper.setAttribute("place", aPlace);
+    }
+
+
+    // Ensure the wrapped item doesn't look like it's in any special state, and
+    // can't be interactved with when in the customization palette.
+    if (aNode.hasAttribute("command")) {
+      wrapper.setAttribute("itemcommand", aNode.getAttribute("command"));
+      aNode.removeAttribute("command");
+    }
+
+    if (aNode.hasAttribute("observes")) {
+      wrapper.setAttribute("itemobserves", aNode.getAttribute("observes"));
+      aNode.removeAttribute("observes");
+    }
+
+    if (aNode.getAttribute("checked") == "true") {
+      wrapper.setAttribute("itemchecked", "true");
+      aNode.removeAttribute("checked");
+    }
+
+    if (aNode.hasAttribute("id")) {
+      wrapper.setAttribute("id", "wrapper-" + aNode.getAttribute("id"));
+    }
+
+    if (aNode.hasAttribute("label")) {
+      wrapper.setAttribute("title", aNode.getAttribute("label"));
+      wrapper.setAttribute("tooltiptext", aNode.getAttribute("label"));
+    } else if (aNode.hasAttribute("title")) {
+      wrapper.setAttribute("title", aNode.getAttribute("title"));
+      wrapper.setAttribute("tooltiptext", aNode.getAttribute("title"));
+    }
+
+    if (aNode.hasAttribute("flex")) {
+      wrapper.setAttribute("flex", aNode.getAttribute("flex"));
+    }
+
+    if (aPlace == "panel") {
+      if (aNode.classList.contains(CustomizableUI.WIDE_PANEL_CLASS)) {
+        wrapper.setAttribute("haswideitem", "true");
+      } else if (wrapper.hasAttribute("haswideitem")) {
+        wrapper.removeAttribute("haswideitem");
+      }
+    }
+
+    let removable = aPlace == "palette" || CustomizableUI.isWidgetRemovable(aNode);
+    wrapper.setAttribute("removable", removable);
+
+    let contextMenuAttrName = "";
+    if (aNode.getAttribute("context")) {
+      contextMenuAttrName = "context";
+    } else if (aNode.getAttribute("contextmenu")) {
+      contextMenuAttrName = "contextmenu";
+    }
+    let currentContextMenu = aNode.getAttribute(contextMenuAttrName);
+    let contextMenuForPlace = aPlace == "panel" ?
+                                kPanelItemContextMenu :
+                                kPaletteItemContextMenu;
+    if (aPlace != "toolbar") {
+      wrapper.setAttribute("context", contextMenuForPlace);
+    }
+    // Only keep track of the menu if it is non-default.
+    if (currentContextMenu &&
+        currentContextMenu != contextMenuForPlace) {
+      aNode.setAttribute("wrapped-context", currentContextMenu);
+      aNode.setAttribute("wrapped-contextAttrName", contextMenuAttrName)
+      aNode.removeAttribute(contextMenuAttrName);
+    } else if (currentContextMenu == contextMenuForPlace) {
+      aNode.removeAttribute(contextMenuAttrName);
+    }
+
+    // Only add listeners for newly created wrappers:
+    if (!aIsUpdate) {
+      wrapper.addEventListener("mousedown", this);
+      wrapper.addEventListener("mouseup", this);
+    }
+
+    return wrapper;
+  },
+
+  deferredUnwrapToolbarItem(aWrapper) {
+    return new Promise(resolve => {
+      dispatchFunction(() => {
+        let item = null;
+        try {
+          item = this.unwrapToolbarItem(aWrapper);
+        } catch (ex) {
+          Cu.reportError(ex);
+        }
+        resolve(item);
+      });
+    });
+  },
+
+  unwrapToolbarItem(aWrapper) {
+    if (aWrapper.nodeName != "toolbarpaletteitem") {
+      return aWrapper;
+    }
+    aWrapper.removeEventListener("mousedown", this);
+    aWrapper.removeEventListener("mouseup", this);
+
+    let place = aWrapper.getAttribute("place");
+
+    let toolbarItem = aWrapper.firstChild;
+    if (!toolbarItem) {
+      log.error("no toolbarItem child for " + aWrapper.tagName + "#" + aWrapper.id);
+      aWrapper.remove();
+      return null;
+    }
+
+    if (aWrapper.hasAttribute("itemobserves")) {
+      toolbarItem.setAttribute("observes", aWrapper.getAttribute("itemobserves"));
+    }
+
+    if (aWrapper.hasAttribute("itemchecked")) {
+      toolbarItem.checked = true;
+    }
+
+    if (aWrapper.hasAttribute("itemcommand")) {
+      let commandID = aWrapper.getAttribute("itemcommand");
+      toolbarItem.setAttribute("command", commandID);
+
+      // XXX Bug 309953 - toolbarbuttons aren't in sync with their commands after customizing
+      let command = this.document.getElementById(commandID);
+      if (command && command.hasAttribute("disabled")) {
+        toolbarItem.setAttribute("disabled", command.getAttribute("disabled"));
+      }
+    }
+
+    let wrappedContext = toolbarItem.getAttribute("wrapped-context");
+    if (wrappedContext) {
+      let contextAttrName = toolbarItem.getAttribute("wrapped-contextAttrName");
+      toolbarItem.setAttribute(contextAttrName, wrappedContext);
+      toolbarItem.removeAttribute("wrapped-contextAttrName");
+      toolbarItem.removeAttribute("wrapped-context");
+    } else if (place == "panel") {
+      toolbarItem.setAttribute("context", kPanelItemContextMenu);
+    }
+
+    if (aWrapper.parentNode) {
+      aWrapper.parentNode.replaceChild(toolbarItem, aWrapper);
+    }
+    return toolbarItem;
+  },
+
+  *_wrapToolbarItem(aArea) {
+    let target = CustomizableUI.getCustomizeTargetForArea(aArea, this.window);
+    if (!target || this.areas.has(target)) {
+      return null;
+    }
+
+    this._addDragHandlers(target);
+    for (let child of target.children) {
+      if (this.isCustomizableItem(child) && !this.isWrappedToolbarItem(child)) {
+        yield this.deferredWrapToolbarItem(child, CustomizableUI.getPlaceForItem(child)).then(null, log.error);
+      }
+    }
+    this.areas.add(target);
+    return target;
+  },
+
+  _wrapToolbarItemSync(aArea) {
+    let target = CustomizableUI.getCustomizeTargetForArea(aArea, this.window);
+    if (!target || this.areas.has(target)) {
+      return null;
+    }
+
+    this._addDragHandlers(target);
+    try {
+      for (let child of target.children) {
+        if (this.isCustomizableItem(child) && !this.isWrappedToolbarItem(child)) {
+          this.wrapToolbarItem(child, CustomizableUI.getPlaceForItem(child));
+        }
+      }
+    } catch (ex) {
+      log.error(ex, ex.stack);
+    }
+
+    this.areas.add(target);
+    return target;
+  },
+
+  *_wrapToolbarItems() {
+    for (let area of CustomizableUI.areas) {
+      yield this._wrapToolbarItem(area);
+    }
+  },
+
+  _addDragHandlers(aTarget) {
+    aTarget.addEventListener("dragstart", this, true);
+    aTarget.addEventListener("dragover", this, true);
+    aTarget.addEventListener("dragexit", this, true);
+    aTarget.addEventListener("drop", this, true);
+    aTarget.addEventListener("dragend", this, true);
+  },
+
+  _wrapItemsInArea(target) {
+    for (let child of target.children) {
+      if (this.isCustomizableItem(child)) {
+        this.wrapToolbarItem(child, CustomizableUI.getPlaceForItem(child));
+      }
+    }
+  },
+
+  _removeDragHandlers(aTarget) {
+    aTarget.removeEventListener("dragstart", this, true);
+    aTarget.removeEventListener("dragover", this, true);
+    aTarget.removeEventListener("dragexit", this, true);
+    aTarget.removeEventListener("drop", this, true);
+    aTarget.removeEventListener("dragend", this, true);
+  },
+
+  _unwrapItemsInArea(target) {
+    for (let toolbarItem of target.children) {
+      if (this.isWrappedToolbarItem(toolbarItem)) {
+        this.unwrapToolbarItem(toolbarItem);
+      }
+    }
+  },
+
+  _unwrapToolbarItems() {
+    return Task.spawn(function*() {
+      for (let target of this.areas) {
+        for (let toolbarItem of target.children) {
+          if (this.isWrappedToolbarItem(toolbarItem)) {
+            yield this.deferredUnwrapToolbarItem(toolbarItem);
+          }
+        }
+        this._removeDragHandlers(target);
+      }
+      this.areas.clear();
+    }.bind(this)).then(null, log.error);
+  },
+
+  _removeExtraToolbarsIfEmpty() {
+    let toolbox = this.window.gNavToolbox;
+    for (let child of toolbox.children) {
+      if (child.hasAttribute("customindex")) {
+        let placements = CustomizableUI.getWidgetIdsInArea(child.id);
+        if (!placements.length) {
+          CustomizableUI.removeExtraToolbar(child.id);
+        }
+      }
+    }
+  },
+
+  persistCurrentSets(aSetBeforePersisting) {
+    let document = this.document;
+    let toolbars = document.querySelectorAll("toolbar[customizable='true'][currentset]");
+    for (let toolbar of toolbars) {
+      if (aSetBeforePersisting) {
+        let set = toolbar.currentSet;
+        toolbar.setAttribute("currentset", set);
+      }
+      // Persist the currentset attribute directly on hardcoded toolbars.
+      document.persist(toolbar.id, "currentset");
+    }
+  },
+
+  reset() {
+    this.resetting = true;
+    // Disable the reset button temporarily while resetting:
+    let btn = this.document.getElementById("customization-reset-button");
+    BrowserUITelemetry.countCustomizationEvent("reset");
+    btn.disabled = true;
+    return Task.spawn(function*() {
+      this._removePanelCustomizationPlaceholders();
+      yield this.depopulatePalette();
+      yield this._unwrapToolbarItems();
+
+      CustomizableUI.reset();
+
+      this._updateLWThemeButtonIcon();
+
+      yield this._wrapToolbarItems();
+      this.populatePalette();
+
+      this.persistCurrentSets(true);
+
+      this._updateResetButton();
+      this._updateUndoResetButton();
+      this._updateEmptyPaletteNotice();
+      this._showPanelCustomizationPlaceholders();
+      this.resetting = false;
+      if (!this._wantToBeInCustomizeMode) {
+        this.exit();
+      }
+    }.bind(this)).then(null, log.error);
+  },
+
+  undoReset() {
+    this.resetting = true;
+
+    return Task.spawn(function*() {
+      this._removePanelCustomizationPlaceholders();
+      yield this.depopulatePalette();
+      yield this._unwrapToolbarItems();
+
+      CustomizableUI.undoReset();
+
+      this._updateLWThemeButtonIcon();
+
+      yield this._wrapToolbarItems();
+      this.populatePalette();
+
+      this.persistCurrentSets(true);
+
+      this._updateResetButton();
+      this._updateUndoResetButton();
+      this._updateEmptyPaletteNotice();
+      this.resetting = false;
+    }.bind(this)).then(null, log.error);
+  },
+
+  _onToolbarVisibilityChange(aEvent) {
+    let toolbar = aEvent.target;
+    if (aEvent.detail.visible && toolbar.getAttribute("customizable") == "true") {
+      toolbar.setAttribute("customizing", "true");
+    } else {
+      toolbar.removeAttribute("customizing");
+    }
+    this._onUIChange();
+    this.updateLWTStyling();
+  },
+
+  onWidgetMoved(aWidgetId, aArea, aOldPosition, aNewPosition) {
+    this._onUIChange();
+  },
+
+  onWidgetAdded(aWidgetId, aArea, aPosition) {
+    this._onUIChange();
+  },
+
+  onWidgetRemoved(aWidgetId, aArea) {
+    this._onUIChange();
+  },
+
+  onWidgetBeforeDOMChange(aNodeToChange, aSecondaryNode, aContainer) {
+    if (aContainer.ownerGlobal != this.window || this.resetting) {
+      return;
+    }
+    if (aContainer.id == CustomizableUI.AREA_PANEL) {
+      this._removePanelCustomizationPlaceholders();
+    }
+    // If we get called for widgets that aren't in the window yet, they might not have
+    // a parentNode at all.
+    if (aNodeToChange.parentNode) {
+      this.unwrapToolbarItem(aNodeToChange.parentNode);
+    }
+    if (aSecondaryNode) {
+      this.unwrapToolbarItem(aSecondaryNode.parentNode);
+    }
+  },
+
+  onWidgetAfterDOMChange(aNodeToChange, aSecondaryNode, aContainer) {
+    if (aContainer.ownerGlobal != this.window || this.resetting) {
+      return;
+    }
+    // If the node is still attached to the container, wrap it again:
+    if (aNodeToChange.parentNode) {
+      let place = CustomizableUI.getPlaceForItem(aNodeToChange);
+      this.wrapToolbarItem(aNodeToChange, place);
+      if (aSecondaryNode) {
+        this.wrapToolbarItem(aSecondaryNode, place);
+      }
+    } else {
+      // If not, it got removed.
+
+      // If an API-based widget is removed while customizing, append it to the palette.
+      // The _applyDrop code itself will take care of positioning it correctly, if
+      // applicable. We need the code to be here so removing widgets using CustomizableUI's
+      // API also does the right thing (and adds it to the palette)
+      let widgetId = aNodeToChange.id;
+      let widget = CustomizableUI.getWidget(widgetId);
+      if (widget.provider == CustomizableUI.PROVIDER_API) {
+        let paletteItem = this.makePaletteItem(widget, "palette");
+        this.visiblePalette.appendChild(paletteItem);
+      }
+    }
+    if (aContainer.id == CustomizableUI.AREA_PANEL) {
+      this._showPanelCustomizationPlaceholders();
+    }
+  },
+
+  onWidgetDestroyed(aWidgetId) {
+    let wrapper = this.document.getElementById("wrapper-" + aWidgetId);
+    if (wrapper) {
+      let wasInPanel = wrapper.parentNode == this.panelUIContents;
+      wrapper.remove();
+      if (wasInPanel) {
+        this._showPanelCustomizationPlaceholders();
+      }
+    }
+  },
+
+  onWidgetAfterCreation(aWidgetId, aArea) {
+    // If the node was added to an area, we would have gotten an onWidgetAdded notification,
+    // plus associated DOM change notifications, so only do stuff for the palette:
+    if (!aArea) {
+      let widgetNode = this.document.getElementById(aWidgetId);
+      if (widgetNode) {
+        this.wrapToolbarItem(widgetNode, "palette");
+      } else {
+        let widget = CustomizableUI.getWidget(aWidgetId);
+        this.visiblePalette.appendChild(this.makePaletteItem(widget, "palette"));
+      }
+    }
+  },
+
+  onAreaNodeRegistered(aArea, aContainer) {
+    if (aContainer.ownerDocument == this.document) {
+      this._wrapItemsInArea(aContainer);
+      this._addDragHandlers(aContainer);
+      DragPositionManager.add(this.window, aArea, aContainer);
+      this.areas.add(aContainer);
+    }
+  },
+
+  onAreaNodeUnregistered(aArea, aContainer, aReason) {
+    if (aContainer.ownerDocument == this.document && aReason == CustomizableUI.REASON_AREA_UNREGISTERED) {
+      this._unwrapItemsInArea(aContainer);
+      this._removeDragHandlers(aContainer);
+      DragPositionManager.remove(this.window, aArea, aContainer);
+      this.areas.delete(aContainer);
+    }
+  },
+
+  openAddonsManagerThemes(aEvent) {
+    aEvent.target.parentNode.parentNode.hidePopup();
+    this.window.BrowserOpenAddonsMgr("addons://list/theme");
+  },
+
+  getMoreThemes(aEvent) {
+    aEvent.target.parentNode.parentNode.hidePopup();
+    let getMoreURL = Services.urlFormatter.formatURLPref("lightweightThemes.getMoreURL");
+    this.window.openUILinkIn(getMoreURL, "tab");
+  },
+
+  onLWThemesMenuShowing(aEvent) {
+    const DEFAULT_THEME_ID = "{972ce4c6-7e08-4474-a285-3208198ce6fd}";
+    const RECENT_LWT_COUNT = 5;
+
+    this._clearLWThemesMenu(aEvent.target);
+
+    function previewTheme(aPreviewThemeEvent) {
+      LightweightThemeManager.previewTheme(
+        aPreviewThemeEvent.target.theme.id != DEFAULT_THEME_ID ?
+        aPreviewThemeEvent.target.theme : null);
+    }
+
+    function resetPreview() {
+      LightweightThemeManager.resetPreview();
+    }
+
+    let onThemeSelected = panel => {
+      this._updateLWThemeButtonIcon();
+      this._onUIChange();
+      panel.hidePopup();
+    };
+
+    AddonManager.getAddonByID(DEFAULT_THEME_ID, function(aDefaultTheme) {
+      let doc = this.window.document;
+
+      function buildToolbarButton(aTheme) {
+        let tbb = doc.createElement("toolbarbutton");
+        tbb.theme = aTheme;
+        tbb.setAttribute("label", aTheme.name);
+        if (aDefaultTheme == aTheme) {
+          // The actual icon is set up so it looks nice in about:addons, but
+          // we'd like the version that's correct for the OS we're on, so we set
+          // an attribute that our styling will then use to display the icon.
+          tbb.setAttribute("defaulttheme", "true");
+        } else {
+          tbb.setAttribute("image", aTheme.iconURL);
+        }
+        if (aTheme.description)
+          tbb.setAttribute("tooltiptext", aTheme.description);
+        tbb.setAttribute("tabindex", "0");
+        tbb.classList.add("customization-lwtheme-menu-theme");
+        tbb.setAttribute("aria-checked", aTheme.isActive);
+        tbb.setAttribute("role", "menuitemradio");
+        if (aTheme.isActive) {
+          tbb.setAttribute("active", "true");
+        }
+        tbb.addEventListener("focus", previewTheme);
+        tbb.addEventListener("mouseover", previewTheme);
+        tbb.addEventListener("blur", resetPreview);
+        tbb.addEventListener("mouseout", resetPreview);
+
+        return tbb;
+      }
+
+      let themes = [aDefaultTheme];
+      let lwts = LightweightThemeManager.usedThemes;
+      let currentLwt = LightweightThemeManager.currentTheme;
+      let currentLwtIndex = lwts.indexOf(currentLwt);
+      if (currentLwtIndex > -1) {
+        // Make sure that the current lightweight theme
+        // is at the beginning of the array to avoid truncation
+        // in the next step.
+        lwts = lwts.splice(currentLwtIndex, 1).concat(lwts);
+      }
+      if (lwts.length > RECENT_LWT_COUNT)
+        lwts.length = RECENT_LWT_COUNT;
+      for (let lwt of lwts) {
+        lwt.isActive = !!currentLwt && (lwt.id == currentLwt.id);
+        themes.push(lwt);
+      }
+
+      let footer = doc.getElementById("customization-lwtheme-menu-footer");
+      let panel = footer.parentNode;
+      let recommendedLabel = doc.getElementById("customization-lwtheme-menu-recommended");
+      for (let theme of themes) {
+        let button = buildToolbarButton(theme);
+        button.addEventListener("command", () => {
+          if ("userDisabled" in button.theme)
+            button.theme.userDisabled = false;
+          else
+            LightweightThemeManager.currentTheme = button.theme;
+          onThemeSelected(panel);
+        });
+        panel.insertBefore(button, recommendedLabel);
+      }
+
+      let lwthemePrefs = Services.prefs.getBranch("lightweightThemes.");
+      let recommendedThemes = lwthemePrefs.getComplexValue("recommendedThemes",
+                                                           Ci.nsISupportsString).data;
+      recommendedThemes = JSON.parse(recommendedThemes);
+      let sb = Services.strings.createBundle("chrome://browser/locale/lightweightThemes.properties");
+      for (let theme of recommendedThemes) {
+        theme.name = sb.GetStringFromName("lightweightThemes." + theme.id + ".name");
+        theme.description = sb.GetStringFromName("lightweightThemes." + theme.id + ".description");
+        let button = buildToolbarButton(theme);
+        button.addEventListener("command", () => {
+          LightweightThemeManager.setLocalTheme(button.theme);
+          recommendedThemes = recommendedThemes.filter((aTheme) => { return aTheme.id != button.theme.id; });
+          let string = Cc["@mozilla.org/supports-string;1"]
+                         .createInstance(Ci.nsISupportsString);
+          string.data = JSON.stringify(recommendedThemes);
+          lwthemePrefs.setComplexValue("recommendedThemes",
+                                       Ci.nsISupportsString, string);
+          onThemeSelected(panel);
+        });
+        panel.insertBefore(button, footer);
+      }
+      let hideRecommendedLabel = (footer.previousSibling == recommendedLabel);
+      recommendedLabel.hidden = hideRecommendedLabel;
+    }.bind(this));
+  },
+
+  _clearLWThemesMenu(panel) {
+    let footer = this.document.getElementById("customization-lwtheme-menu-footer");
+    let recommendedLabel = this.document.getElementById("customization-lwtheme-menu-recommended");
+    for (let element of [footer, recommendedLabel]) {
+      while (element.previousSibling &&
+             element.previousSibling.localName == "toolbarbutton") {
+        element.previousSibling.remove();
+      }
+    }
+
+    // Workaround for bug 1059934
+    panel.removeAttribute("height");
+  },
+
+  _onUIChange() {
+    this._changed = true;
+    if (!this.resetting) {
+      this._updateResetButton();
+      this._updateUndoResetButton();
+      this._updateEmptyPaletteNotice();
+    }
+    CustomizableUI.dispatchToolboxEvent("customizationchange");
+  },
+
+  _updateEmptyPaletteNotice() {
+    let paletteItems = this.visiblePalette.getElementsByTagName("toolbarpaletteitem");
+    this.paletteEmptyNotice.hidden = !!paletteItems.length;
+  },
+
+  _updateResetButton() {
+    let btn = this.document.getElementById("customization-reset-button");
+    btn.disabled = CustomizableUI.inDefaultState;
+  },
+
+  _updateUndoResetButton() {
+    let undoResetButton =  this.document.getElementById("customization-undo-reset-button");
+    undoResetButton.hidden = !CustomizableUI.canUndoReset;
+  },
+
+  handleEvent(aEvent) {
+    switch (aEvent.type) {
+      case "toolbarvisibilitychange":
+        this._onToolbarVisibilityChange(aEvent);
+        break;
+      case "dragstart":
+        this._onDragStart(aEvent);
+        break;
+      case "dragover":
+        this._onDragOver(aEvent);
+        break;
+      case "drop":
+        this._onDragDrop(aEvent);
+        break;
+      case "dragexit":
+        this._onDragExit(aEvent);
+        break;
+      case "dragend":
+        this._onDragEnd(aEvent);
+        break;
+      case "command":
+        if (aEvent.originalTarget == this.window.PanelUI.menuButton) {
+          this.exit();
+          aEvent.preventDefault();
+        }
+        break;
+      case "mousedown":
+        this._onMouseDown(aEvent);
+        break;
+      case "mouseup":
+        this._onMouseUp(aEvent);
+        break;
+      case "keypress":
+        if (aEvent.keyCode == aEvent.DOM_VK_ESCAPE) {
+          this.exit();
+        }
+        break;
+      case "unload":
+        this.uninit();
+        break;
+    }
+  },
+
+  observe(aSubject, aTopic, aData) {
+    switch (aTopic) {
+      case "nsPref:changed":
+        this._updateResetButton();
+        this._updateUndoResetButton();
+#ifdef CAN_DRAW_IN_TITLEBAR
+        this._updateTitlebarButton();
+#endif
+        break;
+      case "lightweight-theme-window-updated":
+        if (aSubject == this.window) {
+          aData = JSON.parse(aData);
+          if (!aData) {
+            this.removeLWTStyling();
+          } else {
+            this.updateLWTStyling(aData);
+          }
+        }
+        break;
+    }
+  },
+
+  _updateTitlebarButton() {
+#ifndef CAN_DRAW_IN_TITLEBAR
+    return;
+#endif
+    let drawInTitlebar = true;
+    try {
+      drawInTitlebar = Services.prefs.getBoolPref(kDrawInTitlebarPref);
+    } catch (ex) { }
+    let button = this.document.getElementById("customization-titlebar-visibility-button");
+    // Drawing in the titlebar means 'hiding' the titlebar:
+    if (drawInTitlebar) {
+      button.removeAttribute("checked");
+    } else {
+      button.setAttribute("checked", "true");
+    }
+  },
+
+  toggleTitlebar(aShouldShowTitlebar) {
+#ifndef CAN_DRAW_IN_TITLEBAR
+    return;
+#endif
+    // Drawing in the titlebar means not showing the titlebar, hence the negation:
+    Services.prefs.setBoolPref(kDrawInTitlebarPref, !aShouldShowTitlebar);
+  },
+
+  _onDragStart(aEvent) {
+    __dumpDragData(aEvent);
+    let item = aEvent.target;
+    while (item && item.localName != "toolbarpaletteitem") {
+      if (item.localName == "toolbar") {
+        return;
+      }
+      item = item.parentNode;
+    }
+
+    let draggedItem = item.firstChild;
+    let placeForItem = CustomizableUI.getPlaceForItem(item);
+    let isRemovable = placeForItem == "palette" ||
+                      CustomizableUI.isWidgetRemovable(draggedItem);
+    if (item.classList.contains(kPlaceholderClass) || !isRemovable) {
+      return;
+    }
+
+    let dt = aEvent.dataTransfer;
+    let documentId = aEvent.target.ownerDocument.documentElement.id;
+    let isInToolbar = placeForItem == "toolbar";
+
+    dt.mozSetDataAt(kDragDataTypePrefix + documentId, draggedItem.id, 0);
+    dt.effectAllowed = "move";
+
+    let itemRect = draggedItem.getBoundingClientRect();
+    let itemCenter = {x: itemRect.left + itemRect.width / 2,
+                      y: itemRect.top + itemRect.height / 2};
+    this._dragOffset = {x: aEvent.clientX - itemCenter.x,
+                        y: aEvent.clientY - itemCenter.y};
+
+    gDraggingInToolbars = new Set();
+
+    // Hack needed so that the dragimage will still show the
+    // item as it appeared before it was hidden.
+    this._initializeDragAfterMove = function() {
+      // For automated tests, we sometimes start exiting customization mode
+      // before this fires, which leaves us with placeholders inserted after
+      // we've exited. So we need to check that we are indeed customizing.
+      if (this._customizing && !this._transitioning) {
+        item.hidden = true;
+        this._showPanelCustomizationPlaceholders();
+        DragPositionManager.start(this.window);
+        if (item.nextSibling) {
+          this._setDragActive(item.nextSibling, "before", draggedItem.id, isInToolbar);
+          this._dragOverItem = item.nextSibling;
+        } else if (isInToolbar && item.previousSibling) {
+          this._setDragActive(item.previousSibling, "after", draggedItem.id, isInToolbar);
+          this._dragOverItem = item.previousSibling;
+        }
+      }
+      this._initializeDragAfterMove = null;
+      this.window.clearTimeout(this._dragInitializeTimeout);
+    }.bind(this);
+    this._dragInitializeTimeout = this.window.setTimeout(this._initializeDragAfterMove, 0);
+  },
+
+  _onDragOver(aEvent) {
+    if (this._isUnwantedDragDrop(aEvent)) {
+      return;
+    }
+    if (this._initializeDragAfterMove) {
+      this._initializeDragAfterMove();
+    }
+
+    __dumpDragData(aEvent);
+
+    let document = aEvent.target.ownerDocument;
+    let documentId = document.documentElement.id;
+    if (!aEvent.dataTransfer.mozTypesAt(0)) {
+      return;
+    }
+
+    let draggedItemId =
+      aEvent.dataTransfer.mozGetDataAt(kDragDataTypePrefix + documentId, 0);
+    let draggedWrapper = document.getElementById("wrapper-" + draggedItemId);
+    let targetArea = this._getCustomizableParent(aEvent.currentTarget);
+    let originArea = this._getCustomizableParent(draggedWrapper);
+
+    // Do nothing if the target or origin are not customizable.
+    if (!targetArea || !originArea) {
+      return;
+    }
+
+    // Do nothing if the widget is not allowed to be removed.
+    if (targetArea.id == kPaletteId &&
+       !CustomizableUI.isWidgetRemovable(draggedItemId)) {
+      return;
+    }
+
+    // Do nothing if the widget is not allowed to move to the target area.
+    if (targetArea.id != kPaletteId &&
+        !CustomizableUI.canWidgetMoveToArea(draggedItemId, targetArea.id)) {
+      return;
+    }
+
+    let targetIsToolbar = CustomizableUI.getAreaType(targetArea.id) == "toolbar";
+    let targetNode = this._getDragOverNode(aEvent, targetArea, targetIsToolbar, draggedItemId);
+
+    // We need to determine the place that the widget is being dropped in
+    // the target.
+    let dragOverItem, dragValue;
+    if (targetNode == targetArea.customizationTarget) {
+      // We'll assume if the user is dragging directly over the target, that
+      // they're attempting to append a child to that target.
+      dragOverItem = (targetIsToolbar ? this._findVisiblePreviousSiblingNode(targetNode.lastChild) :
+                                        targetNode.lastChild) || targetNode;
+      dragValue = "after";
+    } else {
+      let targetParent = targetNode.parentNode;
+      let position = Array.indexOf(targetParent.children, targetNode);
+      if (position == -1) {
+        dragOverItem = targetIsToolbar ? this._findVisiblePreviousSiblingNode(targetNode.lastChild) :
+                                         targetParent.lastChild;
+        dragValue = "after";
+      } else {
+        dragOverItem = targetParent.children[position];
+        if (!targetIsToolbar) {
+          dragValue = "before";
+        } else {
+          // Check if the aDraggedItem is hovered past the first half of dragOverItem
+          let window = dragOverItem.ownerGlobal;
+          let direction = window.getComputedStyle(dragOverItem, null).direction;
+          let itemRect = dragOverItem.getBoundingClientRect();
+          let dropTargetCenter = itemRect.left + (itemRect.width / 2);
+          let existingDir = dragOverItem.getAttribute("dragover");
+          if ((existingDir == "before") == (direction == "ltr")) {
+            dropTargetCenter += (parseInt(dragOverItem.style.borderLeftWidth) || 0) / 2;
+          } else {
+            dropTargetCenter -= (parseInt(dragOverItem.style.borderRightWidth) || 0) / 2;
+          }
+          let before = direction == "ltr" ? aEvent.clientX < dropTargetCenter : aEvent.clientX > dropTargetCenter;
+          dragValue = before ? "before" : "after";
+        }
+      }
+    }
+
+    if (this._dragOverItem && dragOverItem != this._dragOverItem) {
+      this._cancelDragActive(this._dragOverItem, dragOverItem);
+    }
+
+    if (dragOverItem != this._dragOverItem || dragValue != dragOverItem.getAttribute("dragover")) {
+      if (dragOverItem != targetArea.customizationTarget) {
+        this._setDragActive(dragOverItem, dragValue, draggedItemId, targetIsToolbar);
+      } else if (targetIsToolbar) {
+        this._updateToolbarCustomizationOutline(this.window, targetArea);
+      }
+      this._dragOverItem = dragOverItem;
+    }
+
+    aEvent.preventDefault();
+    aEvent.stopPropagation();
+  },
+
+  _onDragDrop(aEvent) {
+    if (this._isUnwantedDragDrop(aEvent)) {
+      return;
+    }
+
+    __dumpDragData(aEvent);
+    this._initializeDragAfterMove = null;
+    this.window.clearTimeout(this._dragInitializeTimeout);
+
+    let targetArea = this._getCustomizableParent(aEvent.currentTarget);
+    let document = aEvent.target.ownerDocument;
+    let documentId = document.documentElement.id;
+    let draggedItemId =
+      aEvent.dataTransfer.mozGetDataAt(kDragDataTypePrefix + documentId, 0);
+    let draggedWrapper = document.getElementById("wrapper-" + draggedItemId);
+    let originArea = this._getCustomizableParent(draggedWrapper);
+    if (this._dragSizeMap) {
+      this._dragSizeMap = new WeakMap();
+    }
+    // Do nothing if the target area or origin area are not customizable.
+    if (!targetArea || !originArea) {
+      return;
+    }
+    let targetNode = this._dragOverItem;
+    let dropDir = targetNode.getAttribute("dragover");
+    // Need to insert *after* this node if we promised the user that:
+    if (targetNode != targetArea && dropDir == "after") {
+      if (targetNode.nextSibling) {
+        targetNode = targetNode.nextSibling;
+      } else {
+        targetNode = targetArea;
+      }
+    }
+    // If the target node is a placeholder, get its sibling as the real target.
+    while (targetNode.classList.contains(kPlaceholderClass) && targetNode.nextSibling) {
+      targetNode = targetNode.nextSibling;
+    }
+    if (targetNode.tagName == "toolbarpaletteitem") {
+      targetNode = targetNode.firstChild;
+    }
+
+    this._cancelDragActive(this._dragOverItem, null, true);
+    this._removePanelCustomizationPlaceholders();
+
+    try {
+      this._applyDrop(aEvent, targetArea, originArea, draggedItemId, targetNode);
+    } catch (ex) {
+      log.error(ex, ex.stack);
+    }
+
+    this._showPanelCustomizationPlaceholders();
+  },
+
+  _applyDrop(aEvent, aTargetArea, aOriginArea, aDraggedItemId, aTargetNode) {
+    let document = aEvent.target.ownerDocument;
+    let draggedItem = document.getElementById(aDraggedItemId);
+    draggedItem.hidden = false;
+    draggedItem.removeAttribute("mousedown");
+
+    // Do nothing if the target was dropped onto itself (ie, no change in area
+    // or position).
+    if (draggedItem == aTargetNode) {
+      return;
+    }
+
+    // Is the target area the customization palette?
+    if (aTargetArea.id == kPaletteId) {
+      // Did we drag from outside the palette?
+      if (aOriginArea.id !== kPaletteId) {
+        if (!CustomizableUI.isWidgetRemovable(aDraggedItemId)) {
+          return;
+        }
+
+        CustomizableUI.removeWidgetFromArea(aDraggedItemId);
+        BrowserUITelemetry.countCustomizationEvent("remove");
+        // Special widgets are removed outright, we can return here:
+        if (CustomizableUI.isSpecialWidget(aDraggedItemId)) {
+          return;
+        }
+      }
+      draggedItem = draggedItem.parentNode;
+
+      // If the target node is the palette itself, just append
+      if (aTargetNode == this.visiblePalette) {
+        this.visiblePalette.appendChild(draggedItem);
+      } else {
+        // The items in the palette are wrapped, so we need the target node's parent here:
+        this.visiblePalette.insertBefore(draggedItem, aTargetNode.parentNode);
+      }
+      if (aOriginArea.id !== kPaletteId) {
+        // The dragend event already fires when the item moves within the palette.
+        this._onDragEnd(aEvent);
+      }
+      return;
+    }
+
+    if (!CustomizableUI.canWidgetMoveToArea(aDraggedItemId, aTargetArea.id)) {
+      return;
+    }
+
+    // Skipintoolbarset items won't really be moved:
+    if (draggedItem.getAttribute("skipintoolbarset") == "true") {
+      // These items should never leave their area:
+      if (aTargetArea != aOriginArea) {
+        return;
+      }
+      let place = draggedItem.parentNode.getAttribute("place");
+      this.unwrapToolbarItem(draggedItem.parentNode);
+      if (aTargetNode == aTargetArea.customizationTarget) {
+        aTargetArea.customizationTarget.appendChild(draggedItem);
+      } else {
+        this.unwrapToolbarItem(aTargetNode.parentNode);
+        aTargetArea.customizationTarget.insertBefore(draggedItem, aTargetNode);
+        this.wrapToolbarItem(aTargetNode, place);
+      }
+      this.wrapToolbarItem(draggedItem, place);
+      BrowserUITelemetry.countCustomizationEvent("move");
+      return;
+    }
+
+    // Is the target the customization area itself? If so, we just add the
+    // widget to the end of the area.
+    if (aTargetNode == aTargetArea.customizationTarget) {
+      CustomizableUI.addWidgetToArea(aDraggedItemId, aTargetArea.id);
+      // For the purposes of BrowserUITelemetry, we consider both moving a widget
+      // within the same area, and adding a widget from one area to another area
+      // as a "move". An "add" is only when we move an item from the palette into
+      // an area.
+      let custEventType = aOriginArea.id == kPaletteId ? "add" : "move";
+      BrowserUITelemetry.countCustomizationEvent(custEventType);
+      this._onDragEnd(aEvent);
+      return;
+    }
+
+    // We need to determine the place that the widget is being dropped in
+    // the target.
+    let placement;
+    let itemForPlacement = aTargetNode;
+    // Skip the skipintoolbarset items when determining the place of the item:
+    while (itemForPlacement && itemForPlacement.getAttribute("skipintoolbarset") == "true" &&
+           itemForPlacement.parentNode &&
+           itemForPlacement.parentNode.nodeName == "toolbarpaletteitem") {
+      itemForPlacement = itemForPlacement.parentNode.nextSibling;
+      if (itemForPlacement && itemForPlacement.nodeName == "toolbarpaletteitem") {
+        itemForPlacement = itemForPlacement.firstChild;
+      }
+    }
+    if (itemForPlacement && !itemForPlacement.classList.contains(kPlaceholderClass)) {
+      let targetNodeId = (itemForPlacement.nodeName == "toolbarpaletteitem") ?
+                            itemForPlacement.firstChild && itemForPlacement.firstChild.id :
+                            itemForPlacement.id;
+      placement = CustomizableUI.getPlacementOfWidget(targetNodeId);
+    }
+    if (!placement) {
+      log.debug("Could not get a position for " + aTargetNode.nodeName + "#" + aTargetNode.id + "." + aTargetNode.className);
+    }
+    let position = placement ? placement.position : null;
+
+    // Is the target area the same as the origin? Since we've already handled
+    // the possibility that the target is the customization palette, we know
+    // that the widget is moving within a customizable area.
+    if (aTargetArea == aOriginArea) {
+      CustomizableUI.moveWidgetWithinArea(aDraggedItemId, position);
+    } else {
+      CustomizableUI.addWidgetToArea(aDraggedItemId, aTargetArea.id, position);
+    }
+
+    this._onDragEnd(aEvent);
+
+    // For BrowserUITelemetry, an "add" is only when we move an item from the palette
+    // into an area. Otherwise, it's a move.
+    let custEventType = aOriginArea.id == kPaletteId ? "add" : "move";
+    BrowserUITelemetry.countCustomizationEvent(custEventType);
+
+    // If we dropped onto a skipintoolbarset item, manually correct the drop location:
+    if (aTargetNode != itemForPlacement) {
+      let draggedWrapper = draggedItem.parentNode;
+      let container = draggedWrapper.parentNode;
+      container.insertBefore(draggedWrapper, aTargetNode.parentNode);
+    }
+  },
+
+  _onDragExit(aEvent) {
+    if (this._isUnwantedDragDrop(aEvent)) {
+      return;
+    }
+
+    __dumpDragData(aEvent);
+
+    // When leaving customization areas, cancel the drag on the last dragover item
+    // We've attached the listener to areas, so aEvent.currentTarget will be the area.
+    // We don't care about dragexit events fired on descendants of the area,
+    // so we check that the event's target is the same as the area to which the listener
+    // was attached.
+    if (this._dragOverItem && aEvent.target == aEvent.currentTarget) {
+      this._cancelDragActive(this._dragOverItem);
+      this._dragOverItem = null;
+    }
+  },
+
+  /**
+   * To workaround bug 460801 we manually forward the drop event here when dragend wouldn't be fired.
+   */
+  _onDragEnd(aEvent) {
+    if (this._isUnwantedDragDrop(aEvent)) {
+      return;
+    }
+    this._initializeDragAfterMove = null;
+    this.window.clearTimeout(this._dragInitializeTimeout);
+    __dumpDragData(aEvent, "_onDragEnd");
+
+    let document = aEvent.target.ownerDocument;
+    document.documentElement.removeAttribute("customizing-movingItem");
+
+    let documentId = document.documentElement.id;
+    if (!aEvent.dataTransfer.mozTypesAt(0)) {
+      return;
+    }
+
+    let draggedItemId =
+      aEvent.dataTransfer.mozGetDataAt(kDragDataTypePrefix + documentId, 0);
+
+    let draggedWrapper = document.getElementById("wrapper-" + draggedItemId);
+
+    // DraggedWrapper might no longer available if a widget node is
+    // destroyed after starting (but before stopping) a drag.
+    if (draggedWrapper) {
+      draggedWrapper.hidden = false;
+      draggedWrapper.removeAttribute("mousedown");
+    }
+
+    if (this._dragOverItem) {
+      this._cancelDragActive(this._dragOverItem);
+      this._dragOverItem = null;
+    }
+    this._updateToolbarCustomizationOutline(this.window);
+    this._showPanelCustomizationPlaceholders();
+    DragPositionManager.stop();
+  },
+
+  _isUnwantedDragDrop(aEvent) {
+    // The simulated events generated by synthesizeDragStart/synthesizeDrop in
+    // mochitests are used only for testing whether the right data is being put
+    // into the dataTransfer. Neither cause a real drop to occur, so they don't
+    // set the source node. There isn't a means of testing real drag and drops,
+    // so this pref skips the check but it should only be set by test code.
+    if (this._skipSourceNodeCheck) {
+      return false;
+    }
+
+    /* Discard drag events that originated from a separate window to
+       prevent content->chrome privilege escalations. */
+    let mozSourceNode = aEvent.dataTransfer.mozSourceNode;
+    // mozSourceNode is null in the dragStart event handler or if
+    // the drag event originated in an external application.
+    return !mozSourceNode ||
+           mozSourceNode.ownerGlobal != this.window;
+  },
+
+  _setDragActive(aItem, aValue, aDraggedItemId, aInToolbar) {
+    if (!aItem) {
+      return;
+    }
+
+    if (aItem.getAttribute("dragover") != aValue) {
+      aItem.setAttribute("dragover", aValue);
+
+      let window = aItem.ownerGlobal;
+      let draggedItem = window.document.getElementById(aDraggedItemId);
+      if (!aInToolbar) {
+        this._setGridDragActive(aItem, draggedItem, aValue);
+      } else {
+        let targetArea = this._getCustomizableParent(aItem);
+        this._updateToolbarCustomizationOutline(window, targetArea);
+        let makeSpaceImmediately = false;
+        if (!gDraggingInToolbars.has(targetArea.id)) {
+          gDraggingInToolbars.add(targetArea.id);
+          let draggedWrapper = this.document.getElementById("wrapper-" + aDraggedItemId);
+          let originArea = this._getCustomizableParent(draggedWrapper);
+          makeSpaceImmediately = originArea == targetArea;
+        }
+        // Calculate width of the item when it'd be dropped in this position
+        let width = this._getDragItemSize(aItem, draggedItem).width;
+        let direction = window.getComputedStyle(aItem).direction;
+        let prop, otherProp;
+        // If we're inserting before in ltr, or after in rtl:
+        if ((aValue == "before") == (direction == "ltr")) {
+          prop = "borderLeftWidth";
+          otherProp = "border-right-width";
+        } else {
+          // otherwise:
+          prop = "borderRightWidth";
+          otherProp = "border-left-width";
+        }
+        if (makeSpaceImmediately) {
+          aItem.setAttribute("notransition", "true");
+        }
+        aItem.style[prop] = width + "px";
+        aItem.style.removeProperty(otherProp);
+        if (makeSpaceImmediately) {
+          // Force a layout flush:
+          aItem.getBoundingClientRect();
+          aItem.removeAttribute("notransition");
+        }
+      }
+    }
+  },
+  _cancelDragActive(aItem, aNextItem, aNoTransition) {
+    this._updateToolbarCustomizationOutline(aItem.ownerGlobal);
+    let currentArea = this._getCustomizableParent(aItem);
+    if (!currentArea) {
+      return;
+    }
+    let isToolbar = CustomizableUI.getAreaType(currentArea.id) == "toolbar";
+    if (isToolbar) {
+      if (aNoTransition) {
+        aItem.setAttribute("notransition", "true");
+      }
+      aItem.removeAttribute("dragover");
+      // Remove both property values in the case that the end padding
+      // had been set.
+      aItem.style.removeProperty("border-left-width");
+      aItem.style.removeProperty("border-right-width");
+      if (aNoTransition) {
+        // Force a layout flush:
+        aItem.getBoundingClientRect();
+        aItem.removeAttribute("notransition");
+      }
+    } else {
+      aItem.removeAttribute("dragover");
+      if (aNextItem) {
+        let nextArea = this._getCustomizableParent(aNextItem);
+        if (nextArea == currentArea) {
+          // No need to do anything if we're still dragging in this area:
+          return;
+        }
+      }
+      // Otherwise, clear everything out:
+      let positionManager = DragPositionManager.getManagerForArea(currentArea);
+      positionManager.clearPlaceholders(currentArea, aNoTransition);
+    }
+  },
+
+  _setGridDragActive(aDragOverNode, aDraggedItem, aValue) {
+    let targetArea = this._getCustomizableParent(aDragOverNode);
+    let draggedWrapper = this.document.getElementById("wrapper-" + aDraggedItem.id);
+    let originArea = this._getCustomizableParent(draggedWrapper);
+    let positionManager = DragPositionManager.getManagerForArea(targetArea);
+    let draggedSize = this._getDragItemSize(aDragOverNode, aDraggedItem);
+    let isWide = aDraggedItem.classList.contains(CustomizableUI.WIDE_PANEL_CLASS);
+    positionManager.insertPlaceholder(targetArea, aDragOverNode, isWide, draggedSize,
+                                      originArea == targetArea);
+  },
+
+  _getDragItemSize(aDragOverNode, aDraggedItem) {
+    // Cache it good, cache it real good.
+    if (!this._dragSizeMap)
+      this._dragSizeMap = new WeakMap();
+    if (!this._dragSizeMap.has(aDraggedItem))
+      this._dragSizeMap.set(aDraggedItem, new WeakMap());
+    let itemMap = this._dragSizeMap.get(aDraggedItem);
+    let targetArea = this._getCustomizableParent(aDragOverNode);
+    let currentArea = this._getCustomizableParent(aDraggedItem);
+    // Return the size for this target from cache, if it exists.
+    let size = itemMap.get(targetArea);
+    if (size)
+      return size;
+
+    // Calculate size of the item when it'd be dropped in this position.
+    let currentParent = aDraggedItem.parentNode;
+    let currentSibling = aDraggedItem.nextSibling;
+    const kAreaType = "cui-areatype";
+    let areaType, currentType;
+
+    if (targetArea != currentArea) {
+      // Move the widget temporarily next to the placeholder.
+      aDragOverNode.parentNode.insertBefore(aDraggedItem, aDragOverNode);
+      // Update the node's areaType.
+      areaType = CustomizableUI.getAreaType(targetArea.id);
+      currentType = aDraggedItem.hasAttribute(kAreaType) &&
+                    aDraggedItem.getAttribute(kAreaType);
+      if (areaType)
+        aDraggedItem.setAttribute(kAreaType, areaType);
+      this.wrapToolbarItem(aDraggedItem, areaType || "palette");
+      CustomizableUI.onWidgetDrag(aDraggedItem.id, targetArea.id);
+    } else {
+      aDraggedItem.parentNode.hidden = false;
+    }
+
+    // Fetch the new size.
+    let rect = aDraggedItem.parentNode.getBoundingClientRect();
+    size = {width: rect.width, height: rect.height};
+    // Cache the found value of size for this target.
+    itemMap.set(targetArea, size);
+
+    if (targetArea != currentArea) {
+      this.unwrapToolbarItem(aDraggedItem.parentNode);
+      // Put the item back into its previous position.
+      currentParent.insertBefore(aDraggedItem, currentSibling);
+      // restore the areaType
+      if (areaType) {
+        if (currentType === false)
+          aDraggedItem.removeAttribute(kAreaType);
+        else
+          aDraggedItem.setAttribute(kAreaType, currentType);
+      }
+      this.createOrUpdateWrapper(aDraggedItem, null, true);
+      CustomizableUI.onWidgetDrag(aDraggedItem.id);
+    } else {
+      aDraggedItem.parentNode.hidden = true;
+    }
+    return size;
+  },
+
+  _getCustomizableParent(aElement) {
+    let areas = CustomizableUI.areas;
+    areas.push(kPaletteId);
+    while (aElement) {
+      if (areas.indexOf(aElement.id) != -1) {
+        return aElement;
+      }
+      aElement = aElement.parentNode;
+    }
+    return null;
+  },
+
+  _getDragOverNode(aEvent, aAreaElement, aInToolbar, aDraggedItemId) {
+    let expectedParent = aAreaElement.customizationTarget || aAreaElement;
+    // Our tests are stupid. Cope:
+    if (!aEvent.clientX && !aEvent.clientY) {
+      return aEvent.target;
+    }
+    // Offset the drag event's position with the offset to the center of
+    // the thing we're dragging
+    let dragX = aEvent.clientX - this._dragOffset.x;
+    let dragY = aEvent.clientY - this._dragOffset.y;
+
+    // Ensure this is within the container
+    let boundsContainer = expectedParent;
+    // NB: because the panel UI itself is inside a scrolling container, we need
+    // to use the parent bounds (otherwise, if the panel UI is scrolled down,
+    // the numbers we get are in window coordinates which leads to various kinds
+    // of weirdness)
+    if (boundsContainer == this.panelUIContents) {
+      boundsContainer = boundsContainer.parentNode;
+    }
+    let bounds = boundsContainer.getBoundingClientRect();
+    dragX = Math.min(bounds.right, Math.max(dragX, bounds.left));
+    dragY = Math.min(bounds.bottom, Math.max(dragY, bounds.top));
+
+    let targetNode;
+    if (aInToolbar) {
+      targetNode = aAreaElement.ownerDocument.elementFromPoint(dragX, dragY);
+      while (targetNode && targetNode.parentNode != expectedParent) {
+        targetNode = targetNode.parentNode;
+      }
+    } else {
+      let positionManager = DragPositionManager.getManagerForArea(aAreaElement);
+      // Make it relative to the container:
+      dragX -= bounds.left;
+      // NB: but if we're in the panel UI, we need to use the actual panel
+      // contents instead of the scrolling container to determine our origin
+      // offset against:
+      if (expectedParent == this.panelUIContents) {
+        dragY -= this.panelUIContents.getBoundingClientRect().top;
+      } else {
+        dragY -= bounds.top;
+      }
+      // Find the closest node:
+      targetNode = positionManager.find(aAreaElement, dragX, dragY, aDraggedItemId);
+    }
+    return targetNode || aEvent.target;
+  },
+
+  _onMouseDown(aEvent) {
+    log.debug("_onMouseDown");
+    if (aEvent.button != 0) {
+      return;
+    }
+    let doc = aEvent.target.ownerDocument;
+    doc.documentElement.setAttribute("customizing-movingItem", true);
+    let item = this._getWrapper(aEvent.target);
+    if (item && !item.classList.contains(kPlaceholderClass) &&
+        item.getAttribute("removable") == "true") {
+      item.setAttribute("mousedown", "true");
+    }
+  },
+
+  _onMouseUp(aEvent) {
+    log.debug("_onMouseUp");
+    if (aEvent.button != 0) {
+      return;
+    }
+    let doc = aEvent.target.ownerDocument;
+    doc.documentElement.removeAttribute("customizing-movingItem");
+    let item = this._getWrapper(aEvent.target);
+    if (item) {
+      item.removeAttribute("mousedown");
+    }
+  },
+
+  _getWrapper(aElement) {
+    while (aElement && aElement.localName != "toolbarpaletteitem") {
+      if (aElement.localName == "toolbar")
+        return null;
+      aElement = aElement.parentNode;
+    }
+    return aElement;
+  },
+
+  _showPanelCustomizationPlaceholders() {
+    let doc = this.document;
+    let contents = this.panelUIContents;
+    let narrowItemsAfterWideItem = 0;
+    let node = contents.lastChild;
+    while (node && !node.classList.contains(CustomizableUI.WIDE_PANEL_CLASS) &&
+           (!node.firstChild || !node.firstChild.classList.contains(CustomizableUI.WIDE_PANEL_CLASS))) {
+      if (!node.hidden && !node.classList.contains(kPlaceholderClass)) {
+        narrowItemsAfterWideItem++;
+      }
+      node = node.previousSibling;
+    }
+
+    let orphanedItems = narrowItemsAfterWideItem % CustomizableUI.PANEL_COLUMN_COUNT;
+    let placeholders = CustomizableUI.PANEL_COLUMN_COUNT - orphanedItems;
+
+    let currentPlaceholderCount = contents.querySelectorAll("." + kPlaceholderClass).length;
+    if (placeholders > currentPlaceholderCount) {
+      while (placeholders-- > currentPlaceholderCount) {
+        let placeholder = doc.createElement("toolbarpaletteitem");
+        placeholder.classList.add(kPlaceholderClass);
+        // XXXjaws The toolbarbutton child here is only necessary to get
+        //  the styling right here.
+        let placeholderChild = doc.createElement("toolbarbutton");
+        placeholderChild.classList.add(kPlaceholderClass + "-child");
+        placeholder.appendChild(placeholderChild);
+        contents.appendChild(placeholder);
+      }
+    } else if (placeholders < currentPlaceholderCount) {
+      while (placeholders++ < currentPlaceholderCount) {
+        contents.querySelectorAll("." + kPlaceholderClass)[0].remove();
+      }
+    }
+  },
+
+  _removePanelCustomizationPlaceholders() {
+    let contents = this.panelUIContents;
+    let oldPlaceholders = contents.getElementsByClassName(kPlaceholderClass);
+    while (oldPlaceholders.length) {
+      contents.removeChild(oldPlaceholders[0]);
+    }
+  },
+
+  /**
+   * Update toolbar customization targets during drag events to add or remove
+   * outlines to indicate that an area is customizable.
+   *
+   * @param aWindow                       The XUL window in which outlines should be updated.
+   * @param {Element} [aToolbarArea=null] The element of the customizable toolbar area to add the
+   *                                      outline to. If aToolbarArea is falsy, the outline will be
+   *                                      removed from all toolbar areas.
+   */
+  _updateToolbarCustomizationOutline(aWindow, aToolbarArea = null) {
+    // Remove the attribute from existing customization targets
+    for (let area of CustomizableUI.areas) {
+      if (CustomizableUI.getAreaType(area) != CustomizableUI.TYPE_TOOLBAR) {
+        continue;
+      }
+      let target = CustomizableUI.getCustomizeTargetForArea(area, aWindow);
+      target.removeAttribute("customizing-dragovertarget");
+    }
+
+    // Now set the attribute on the desired target
+    if (aToolbarArea) {
+      if (CustomizableUI.getAreaType(aToolbarArea.id) != CustomizableUI.TYPE_TOOLBAR)
+        return;
+      let target = CustomizableUI.getCustomizeTargetForArea(aToolbarArea.id, aWindow);
+      target.setAttribute("customizing-dragovertarget", true);
+    }
+  },
+
+  _findVisiblePreviousSiblingNode(aReferenceNode) {
+    while (aReferenceNode &&
+           aReferenceNode.localName == "toolbarpaletteitem" &&
+           aReferenceNode.firstChild.hidden) {
+      aReferenceNode = aReferenceNode.previousSibling;
+    }
+    return aReferenceNode;
+  },
+};
+
+function __dumpDragData(aEvent, caller) {
+  if (!gDebug) {
+    return;
+  }
+  let str = "Dumping drag data (" + (caller ? caller + " in " : "") + "CustomizeMode.jsm) {\n";
+  str += "  type: " + aEvent["type"] + "\n";
+  for (let el of ["target", "currentTarget", "relatedTarget"]) {
+    if (aEvent[el]) {
+      str += "  " + el + ": " + aEvent[el] + "(localName=" + aEvent[el].localName + "; id=" + aEvent[el].id + ")\n";
+    }
+  }
+  for (let prop in aEvent.dataTransfer) {
+    if (typeof aEvent.dataTransfer[prop] != "function") {
+      str += "  dataTransfer[" + prop + "]: " + aEvent.dataTransfer[prop] + "\n";
+    }
+  }
+  str += "}";
+  log.debug(str);
+}
+
+function dispatchFunction(aFunc) {
+  Services.tm.currentThread.dispatch(aFunc, Ci.nsIThread.DISPATCH_NORMAL);
+}
diff --git a/application/basilisk/components/customizableui/DragPositionManager.jsm b/application/basilisk/components/customizableui/DragPositionManager.jsm
new file mode 100644
index 000000000..65e2585a5
--- /dev/null
+++ b/application/basilisk/components/customizableui/DragPositionManager.jsm
@@ -0,0 +1,420 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+Components.utils.import("resource:///modules/CustomizableUI.jsm");
+
+var gManagers = new WeakMap();
+
+const kPaletteId = "customization-palette";
+const kPlaceholderClass = "panel-customization-placeholder";
+
+this.EXPORTED_SYMBOLS = ["DragPositionManager"];
+
+function AreaPositionManager(aContainer) {
+  // Caching the direction and bounds of the container for quick access later:
+  let window = aContainer.ownerGlobal;
+  this._dir = window.getComputedStyle(aContainer).direction;
+  let containerRect = aContainer.getBoundingClientRect();
+  this._containerInfo = {
+    left: containerRect.left,
+    right: containerRect.right,
+    top: containerRect.top,
+    width: containerRect.width
+  };
+  this._inPanel = aContainer.id == CustomizableUI.AREA_PANEL;
+  this._horizontalDistance = null;
+  this.update(aContainer);
+}
+
+AreaPositionManager.prototype = {
+  _nodePositionStore: null,
+  _wideCache: null,
+
+  update(aContainer) {
+    this._nodePositionStore = new WeakMap();
+    this._wideCache = new Set();
+    let last = null;
+    let singleItemHeight;
+    for (let child of aContainer.children) {
+      if (child.hidden) {
+        continue;
+      }
+      let isNodeWide = this._checkIfWide(child);
+      if (isNodeWide) {
+        this._wideCache.add(child.id);
+      }
+      let coordinates = this._lazyStoreGet(child);
+      // We keep a baseline horizontal distance between non-wide nodes around
+      // for use when we can't compare with previous/next nodes
+      if (!this._horizontalDistance && last && !isNodeWide) {
+        this._horizontalDistance = coordinates.left - last.left;
+      }
+      // We also keep the basic height of non-wide items for use below:
+      if (!isNodeWide && !singleItemHeight) {
+        singleItemHeight = coordinates.height;
+      }
+      last = !isNodeWide ? coordinates : null;
+    }
+    if (this._inPanel) {
+      this._heightToWidthFactor = CustomizableUI.PANEL_COLUMN_COUNT;
+    } else {
+      this._heightToWidthFactor = this._containerInfo.width / singleItemHeight;
+    }
+  },
+
+  /**
+   * Find the closest node in the container given the coordinates.
+   * "Closest" is defined in a somewhat strange manner: we prefer nodes
+   * which are in the same row over nodes that are in a different row.
+   * In order to implement this, we use a weighted cartesian distance
+   * where dy is more heavily weighted by a factor corresponding to the
+   * ratio between the container's width and the height of its elements.
+   */
+  find(aContainer, aX, aY, aDraggedItemId) {
+    let closest = null;
+    let minCartesian = Number.MAX_VALUE;
+    let containerX = this._containerInfo.left;
+    let containerY = this._containerInfo.top;
+    for (let node of aContainer.children) {
+      let coordinates = this._lazyStoreGet(node);
+      let offsetX = coordinates.x - containerX;
+      let offsetY = coordinates.y - containerY;
+      let hDiff = offsetX - aX;
+      let vDiff = offsetY - aY;
+      // For wide widgets, we're always going to be further from the center
+      // horizontally. Compensate:
+      if (this.isWide(node)) {
+        hDiff /= CustomizableUI.PANEL_COLUMN_COUNT;
+      }
+      // Then compensate for the height/width ratio so that we prefer items
+      // which are in the same row:
+      hDiff /= this._heightToWidthFactor;
+
+      let cartesianDiff = hDiff * hDiff + vDiff * vDiff;
+      if (cartesianDiff < minCartesian) {
+        minCartesian = cartesianDiff;
+        closest = node;
+      }
+    }
+
+    // Now correct this node based on what we're dragging
+    if (closest) {
+      let doc = aContainer.ownerDocument;
+      let draggedItem = doc.getElementById(aDraggedItemId);
+      // If dragging a wide item, always pick the first item in a row:
+      if (this._inPanel && draggedItem &&
+          draggedItem.classList.contains(CustomizableUI.WIDE_PANEL_CLASS)) {
+        return this._firstInRow(closest);
+      }
+      let targetBounds = this._lazyStoreGet(closest);
+      let farSide = this._dir == "ltr" ? "right" : "left";
+      let outsideX = targetBounds[farSide];
+      // Check if we're closer to the next target than to this one:
+      // Only move if we're not targeting a node in a different row:
+      if (aY > targetBounds.top && aY < targetBounds.bottom) {
+        if ((this._dir == "ltr" && aX > outsideX) ||
+            (this._dir == "rtl" && aX < outsideX)) {
+          return closest.nextSibling || aContainer;
+        }
+      }
+    }
+    return closest;
+  },
+
+  /**
+   * "Insert" a "placeholder" by shifting the subsequent children out of the
+   * way. We go through all the children, and shift them based on the position
+   * they would have if we had inserted something before aBefore. We use CSS
+   * transforms for this, which are CSS transitioned.
+   */
+  insertPlaceholder(aContainer, aBefore, aWide, aSize, aIsFromThisArea) {
+    let isShifted = false;
+    let shiftDown = aWide;
+    for (let child of aContainer.children) {
+      // Don't need to shift hidden nodes:
+      if (child.getAttribute("hidden") == "true") {
+        continue;
+      }
+      // If this is the node before which we're inserting, start shifting
+      // everything that comes after. One exception is inserting at the end
+      // of the menupanel, in which case we do not shift the placeholders:
+      if (child == aBefore && !child.classList.contains(kPlaceholderClass)) {
+        isShifted = true;
+        // If the node before which we're inserting is wide, we should
+        // shift everything one row down:
+        if (!shiftDown && this.isWide(child)) {
+          shiftDown = true;
+        }
+      }
+      // If we're moving items before a wide node that were already there,
+      // it's possible it's not necessary to shift nodes
+      // including & after the wide node.
+      if (this.__undoShift) {
+        isShifted = false;
+      }
+      if (isShifted) {
+        // Conversely, if we're adding something before a wide node, for
+        // simplicity's sake we move everything including the wide node down:
+        if (this.__moveDown) {
+          shiftDown = true;
+        }
+        if (aIsFromThisArea && !this._lastPlaceholderInsertion) {
+          child.setAttribute("notransition", "true");
+        }
+        // Determine the CSS transform based on the next node:
+        child.style.transform = this._getNextPos(child, shiftDown, aSize);
+      } else {
+        // If we're not shifting this node, reset the transform
+        child.style.transform = "";
+      }
+    }
+    if (aContainer.lastChild && aIsFromThisArea &&
+        !this._lastPlaceholderInsertion) {
+      // Flush layout:
+      aContainer.lastChild.getBoundingClientRect();
+      // then remove all the [notransition]
+      for (let child of aContainer.children) {
+        child.removeAttribute("notransition");
+      }
+    }
+    delete this.__moveDown;
+    delete this.__undoShift;
+    this._lastPlaceholderInsertion = aBefore;
+  },
+
+  isWide(aNode) {
+    return this._wideCache.has(aNode.id);
+  },
+
+  _checkIfWide(aNode) {
+    return this._inPanel && aNode && aNode.firstChild &&
+           aNode.firstChild.classList.contains(CustomizableUI.WIDE_PANEL_CLASS);
+  },
+
+  /**
+   * Reset all the transforms in this container, optionally without
+   * transitioning them.
+   * @param aContainer    the container in which to reset transforms
+   * @param aNoTransition if truthy, adds a notransition attribute to the node
+   *                      while resetting the transform.
+   */
+  clearPlaceholders(aContainer, aNoTransition) {
+    for (let child of aContainer.children) {
+      if (aNoTransition) {
+        child.setAttribute("notransition", true);
+      }
+      child.style.transform = "";
+      if (aNoTransition) {
+        // Need to force a reflow otherwise this won't work.
+        child.getBoundingClientRect();
+        child.removeAttribute("notransition");
+      }
+    }
+    // We snapped back, so we can assume there's no more
+    // "last" placeholder insertion point to keep track of.
+    if (aNoTransition) {
+      this._lastPlaceholderInsertion = null;
+    }
+  },
+
+  _getNextPos(aNode, aShiftDown, aSize) {
+    // Shifting down is easy:
+    if (this._inPanel && aShiftDown) {
+      return "translate(0, " + aSize.height + "px)";
+    }
+    return this._diffWithNext(aNode, aSize);
+  },
+
+  _diffWithNext(aNode, aSize) {
+    let xDiff;
+    let yDiff = null;
+    let nodeBounds = this._lazyStoreGet(aNode);
+    let side = this._dir == "ltr" ? "left" : "right";
+    let next = this._getVisibleSiblingForDirection(aNode, "next");
+    // First we determine the transform along the x axis.
+    // Usually, there will be a next node to base this on:
+    if (next) {
+      let otherBounds = this._lazyStoreGet(next);
+      xDiff = otherBounds[side] - nodeBounds[side];
+      // If the next node is a wide item in the panel, check if we could maybe
+      // just move further out in the same row, without snapping to the next
+      // one. This happens, for example, if moving an item that's before a wide
+      // node within its own row of items. There will be space to drop this
+      // item within the row, and the rest of the items do not need to shift.
+      if (this.isWide(next)) {
+        let otherXDiff = this._moveNextBasedOnPrevious(aNode, nodeBounds,
+                                                       this._firstInRow(aNode));
+        // If this has the same sign as our original shift, we're still
+        // snapping to the start of the row. In this case, we should move
+        // everything after us a row down, so as not to display two nodes on
+        // top of each other:
+        // (we would be able to get away with checking for equality instead of
+        //  equal signs here, but one of these is based on the x coordinate of
+        //  the first item in row N and one on that for row N - 1, so this is
+        //  safer, as their margins might differ)
+        if ((otherXDiff < 0) == (xDiff < 0)) {
+          this.__moveDown = true;
+        } else {
+          // Otherwise, we succeeded and can move further out. This also means
+          // we can stop shifting the rest of the content:
+          xDiff = otherXDiff;
+          this.__undoShift = true;
+        }
+      } else {
+        // We set this explicitly because otherwise some strange difference
+        // between the height and the actual difference between line creeps in
+        // and messes with alignments
+        yDiff = otherBounds.top - nodeBounds.top;
+      }
+    } else {
+      // We don't have a sibling whose position we can use. First, let's see
+      // if we're also the first item (which complicates things):
+      let firstNode = this._firstInRow(aNode);
+      if (aNode == firstNode) {
+        // Maybe we stored the horizontal distance between non-wide nodes,
+        // if not, we'll use the width of the incoming node as a proxy:
+        xDiff = this._horizontalDistance || aSize.width;
+      } else {
+        // If not, we should be able to get the distance to the previous node
+        // and use the inverse, unless there's no room for another node (ie we
+        // are the last node and there's no room for another one)
+        xDiff = this._moveNextBasedOnPrevious(aNode, nodeBounds, firstNode);
+      }
+    }
+
+    // If we've not determined the vertical difference yet, check it here
+    if (yDiff === null) {
+      // If the next node is behind rather than in front, we must have moved
+      // vertically:
+      if ((xDiff > 0 && this._dir == "rtl") || (xDiff < 0 && this._dir == "ltr")) {
+        yDiff = aSize.height;
+      } else {
+        // Otherwise, we haven't
+        yDiff = 0;
+      }
+    }
+    return "translate(" + xDiff + "px, " + yDiff + "px)";
+  },
+
+  /**
+   * Helper function to find the transform a node if there isn't a next node
+   * to base that on.
+   * @param aNode           the node to transform
+   * @param aNodeBounds     the bounding rect info of this node
+   * @param aFirstNodeInRow the first node in aNode's row
+   */
+  _moveNextBasedOnPrevious(aNode, aNodeBounds, aFirstNodeInRow) {
+    let next = this._getVisibleSiblingForDirection(aNode, "previous");
+    let otherBounds = this._lazyStoreGet(next);
+    let side = this._dir == "ltr" ? "left" : "right";
+    let xDiff = aNodeBounds[side] - otherBounds[side];
+    // If, however, this means we move outside the container's box
+    // (i.e. the row in which this item is placed is full)
+    // we should move it to align with the first item in the next row instead
+    let bound = this._containerInfo[this._dir == "ltr" ? "right" : "left"];
+    if ((this._dir == "ltr" && xDiff + aNodeBounds.right > bound) ||
+        (this._dir == "rtl" && xDiff + aNodeBounds.left < bound)) {
+      xDiff = this._lazyStoreGet(aFirstNodeInRow)[side] - aNodeBounds[side];
+    }
+    return xDiff;
+  },
+
+  /**
+   * Get position details from our cache. If the node is not yet cached, get its position
+   * information and cache it now.
+   * @param aNode  the node whose position info we want
+   * @return the position info
+   */
+  _lazyStoreGet(aNode) {
+    let rect = this._nodePositionStore.get(aNode);
+    if (!rect) {
+      // getBoundingClientRect() returns a DOMRect that is live, meaning that
+      // as the element moves around, the rects values change. We don't want
+      // that - we want a snapshot of what the rect values are right at this
+      // moment, and nothing else. So we have to clone the values.
+      let clientRect = aNode.getBoundingClientRect();
+      rect = {
+        left: clientRect.left,
+        right: clientRect.right,
+        width: clientRect.width,
+        height: clientRect.height,
+        top: clientRect.top,
+        bottom: clientRect.bottom,
+      };
+      rect.x = rect.left + rect.width / 2;
+      rect.y = rect.top + rect.height / 2;
+      Object.freeze(rect);
+      this._nodePositionStore.set(aNode, rect);
+    }
+    return rect;
+  },
+
+  _firstInRow(aNode) {
+    // XXXmconley: I'm not entirely sure why we need to take the floor of these
+    // values - it looks like, periodically, we're getting fractional pixels back
+    // from lazyStoreGet. I've filed bug 994247 to investigate.
+    let bound = Math.floor(this._lazyStoreGet(aNode).top);
+    let rv = aNode;
+    let prev;
+    while (rv && (prev = this._getVisibleSiblingForDirection(rv, "previous"))) {
+      if (Math.floor(this._lazyStoreGet(prev).bottom) <= bound) {
+        return rv;
+      }
+      rv = prev;
+    }
+    return rv;
+  },
+
+  _getVisibleSiblingForDirection(aNode, aDirection) {
+    let rv = aNode;
+    do {
+      rv = rv[aDirection + "Sibling"];
+    } while (rv && rv.getAttribute("hidden") == "true")
+    return rv;
+  }
+}
+
+var DragPositionManager = {
+  start(aWindow) {
+    let areas = CustomizableUI.areas.filter((area) => CustomizableUI.getAreaType(area) != "toolbar");
+    areas = areas.map((area) => CustomizableUI.getCustomizeTargetForArea(area, aWindow));
+    areas.push(aWindow.document.getElementById(kPaletteId));
+    for (let areaNode of areas) {
+      let positionManager = gManagers.get(areaNode);
+      if (positionManager) {
+        positionManager.update(areaNode);
+      } else {
+        gManagers.set(areaNode, new AreaPositionManager(areaNode));
+      }
+    }
+  },
+
+  add(aWindow, aArea, aContainer) {
+    if (CustomizableUI.getAreaType(aArea) != "toolbar") {
+      return;
+    }
+
+    gManagers.set(aContainer, new AreaPositionManager(aContainer));
+  },
+
+  remove(aWindow, aArea, aContainer) {
+    if (CustomizableUI.getAreaType(aArea) != "toolbar") {
+      return;
+    }
+
+    gManagers.delete(aContainer);
+  },
+
+  stop() {
+    gManagers = new WeakMap();
+  },
+
+  getManagerForArea(aArea) {
+    return gManagers.get(aArea);
+  }
+};
+
+Object.freeze(DragPositionManager);
diff --git a/application/basilisk/components/customizableui/PanelWideWidgetTracker.jsm b/application/basilisk/components/customizableui/PanelWideWidgetTracker.jsm
new file mode 100644
index 000000000..a9b38c23e
--- /dev/null
+++ b/application/basilisk/components/customizableui/PanelWideWidgetTracker.jsm
@@ -0,0 +1,172 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;
+
+this.EXPORTED_SYMBOLS = ["PanelWideWidgetTracker"];
+
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "CustomizableUI",
+  "resource:///modules/CustomizableUI.jsm");
+
+var gPanel = CustomizableUI.AREA_PANEL;
+// We keep track of the widget placements for the panel locally:
+var gPanelPlacements = [];
+
+// All the wide widgets we know of:
+var gWideWidgets = new Set();
+// All the widgets we know of:
+var gSeenWidgets = new Set();
+
+var PanelWideWidgetTracker = {
+  // Listeners used to validate panel contents whenever they change:
+  onWidgetAdded(aWidgetId, aArea, aPosition) {
+    if (aArea == gPanel) {
+      gPanelPlacements = CustomizableUI.getWidgetIdsInArea(gPanel);
+      let moveForward = this.shouldMoveForward(aWidgetId, aPosition);
+      this.adjustWidgets(aWidgetId, moveForward);
+    }
+  },
+  onWidgetMoved(aWidgetId, aArea, aOldPosition, aNewPosition) {
+    if (aArea == gPanel) {
+      gPanelPlacements = CustomizableUI.getWidgetIdsInArea(gPanel);
+      let moveForward = this.shouldMoveForward(aWidgetId, aNewPosition);
+      this.adjustWidgets(aWidgetId, moveForward);
+    }
+  },
+  onWidgetRemoved(aWidgetId, aPrevArea) {
+    if (aPrevArea == gPanel) {
+      gPanelPlacements = CustomizableUI.getWidgetIdsInArea(gPanel);
+      this.adjustWidgets(aWidgetId, false);
+    }
+  },
+  onWidgetReset(aWidgetId) {
+    gPanelPlacements = CustomizableUI.getWidgetIdsInArea(gPanel);
+  },
+  // Listener to keep abreast of any new nodes. We use the DOM one because
+  // we need access to the actual node's classlist, so we can't use the ones above.
+  // Furthermore, onWidgetCreated only fires for API-based widgets, not for XUL ones.
+  onWidgetAfterDOMChange(aNode, aNextNode, aContainer) {
+    if (!gSeenWidgets.has(aNode.id)) {
+      if (aNode.classList.contains(CustomizableUI.WIDE_PANEL_CLASS)) {
+        gWideWidgets.add(aNode.id);
+      }
+      gSeenWidgets.add(aNode.id);
+    }
+  },
+  // When widgets get destroyed, we remove them from our sets of stuff we care about:
+  onWidgetDestroyed(aWidgetId) {
+    gSeenWidgets.delete(aWidgetId);
+    gWideWidgets.delete(aWidgetId);
+  },
+  shouldMoveForward(aWidgetId, aPosition) {
+    let currentWidgetAtPosition = gPanelPlacements[aPosition + 1];
+    let rv = gWideWidgets.has(currentWidgetAtPosition) && !gWideWidgets.has(aWidgetId);
+    // We might now think we can move forward, but for that we need at least 2 more small
+    // widgets to be present:
+    if (rv) {
+      let furtherWidgets = gPanelPlacements.slice(aPosition + 2);
+      let realWidgets = 0;
+      if (furtherWidgets.length >= 2) {
+        while (furtherWidgets.length && realWidgets < 2) {
+          let w = furtherWidgets.shift();
+          if (!gWideWidgets.has(w) && this.checkWidgetStatus(w)) {
+            realWidgets++;
+          }
+        }
+      }
+      if (realWidgets < 2) {
+        rv = false;
+      }
+    }
+    return rv;
+  },
+  adjustWidgets(aWidgetId, aMoveForwards) {
+    if (this.adjusting) {
+      return;
+    }
+    this.adjusting = true;
+    let widgetsAffected = gPanelPlacements.filter((w) => gWideWidgets.has(w));
+    // If we're moving the wide widgets forwards (down/to the right in the panel)
+    // we want to start with the last widgets. Otherwise we move widgets over other wide
+    // widgets, which might mess up their order. Likewise, if moving backwards we should start with
+    // the first widget and work our way down/right from there.
+    let compareFn = aMoveForwards ? ((a, b) => a < b) : ((a, b) => a > b);
+    widgetsAffected.sort((a, b) => compareFn(gPanelPlacements.indexOf(a),
+                                             gPanelPlacements.indexOf(b)));
+    for (let widget of widgetsAffected) {
+      this.adjustPosition(widget, aMoveForwards);
+    }
+    this.adjusting = false;
+  },
+  // This function is called whenever an item gets moved in the menu panel. It
+  // adjusts the position of widgets within the panel to prevent "gaps" between
+  // wide widgets that could be filled up with single column widgets
+  adjustPosition(aWidgetId, aMoveForwards) {
+    // Make sure that there are n % columns = 0 narrow buttons before the widget.
+    let placementIndex = gPanelPlacements.indexOf(aWidgetId);
+    let prevSiblingCount = 0;
+    let fixedPos = null;
+    while (placementIndex--) {
+      let thisWidgetId = gPanelPlacements[placementIndex];
+      if (gWideWidgets.has(thisWidgetId)) {
+        continue;
+      }
+      let widgetStatus = this.checkWidgetStatus(thisWidgetId);
+      if (!widgetStatus) {
+        continue;
+      }
+      if (widgetStatus == "public-only") {
+        fixedPos = !fixedPos ? placementIndex : Math.min(fixedPos, placementIndex);
+        prevSiblingCount = 0;
+      } else {
+        prevSiblingCount++;
+      }
+    }
+
+    if (fixedPos !== null || prevSiblingCount % CustomizableUI.PANEL_COLUMN_COUNT) {
+      let desiredPos = (fixedPos !== null) ? fixedPos : gPanelPlacements.indexOf(aWidgetId);
+      let desiredChange = -(prevSiblingCount % CustomizableUI.PANEL_COLUMN_COUNT);
+      if (aMoveForwards && fixedPos == null) {
+        // +1 because otherwise we'd count ourselves:
+        desiredChange = CustomizableUI.PANEL_COLUMN_COUNT + desiredChange + 1;
+      }
+      desiredPos += desiredChange;
+      CustomizableUI.moveWidgetWithinArea(aWidgetId, desiredPos);
+    }
+  },
+
+  /*
+   * Check whether a widget id is actually known anywhere.
+   * @returns false if the widget doesn't exist,
+   *          "public-only" if it's not shown in private windows
+   *          "real" if it does exist and is shown even in private windows
+   */
+  checkWidgetStatus(aWidgetId) {
+    let widgetWrapper = CustomizableUI.getWidget(aWidgetId);
+    // This widget might not actually exist:
+    if (!widgetWrapper) {
+      return false;
+    }
+    // This widget might still not actually exist:
+    if (widgetWrapper.provider == CustomizableUI.PROVIDER_XUL &&
+        widgetWrapper.instances.length == 0) {
+      return false;
+    }
+
+    // Or it might only be there some of the time:
+    if (widgetWrapper.provider == CustomizableUI.PROVIDER_API &&
+        widgetWrapper.showInPrivateBrowsing === false) {
+      return "public-only";
+    }
+    return "real";
+  },
+
+  init() {
+    // Initialize our local placements copy and register the listener
+    gPanelPlacements = CustomizableUI.getWidgetIdsInArea(gPanel);
+    CustomizableUI.addListener(this);
+  },
+};
diff --git a/application/basilisk/components/customizableui/ScrollbarSampler.jsm b/application/basilisk/components/customizableui/ScrollbarSampler.jsm
new file mode 100644
index 000000000..5a2bfd3e0
--- /dev/null
+++ b/application/basilisk/components/customizableui/ScrollbarSampler.jsm
@@ -0,0 +1,65 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+this.EXPORTED_SYMBOLS = ["ScrollbarSampler"];
+
+const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;
+
+Cu.import("resource://gre/modules/Services.jsm");
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+
+var gSystemScrollbarWidth = null;
+
+this.ScrollbarSampler = {
+  getSystemScrollbarWidth() {
+    if (gSystemScrollbarWidth !== null) {
+      return Promise.resolve(gSystemScrollbarWidth);
+    }
+
+    return new Promise(resolve => {
+      this._sampleSystemScrollbarWidth().then(function(systemScrollbarWidth) {
+        gSystemScrollbarWidth = systemScrollbarWidth;
+        resolve(gSystemScrollbarWidth);
+      });
+    });
+  },
+
+  resetSystemScrollbarWidth() {
+    gSystemScrollbarWidth = null;
+  },
+
+  _sampleSystemScrollbarWidth() {
+    let hwin = Services.appShell.hiddenDOMWindow;
+    let hdoc = hwin.document.documentElement;
+    let iframe = hwin.document.createElementNS("http://www.w3.org/1999/xhtml",
+                                               "html:iframe");
+    iframe.setAttribute("srcdoc", '<body style="overflow-y: scroll"></body>');
+    hdoc.appendChild(iframe);
+
+    let cwindow = iframe.contentWindow;
+    let utils = cwindow.QueryInterface(Ci.nsIInterfaceRequestor)
+                       .getInterface(Ci.nsIDOMWindowUtils);
+
+    return new Promise(resolve => {
+      cwindow.addEventListener("load", function onLoad(aEvent) {
+        cwindow.removeEventListener("load", onLoad);
+        let sbWidth = {};
+        try {
+          utils.getScrollbarSize(true, sbWidth, {});
+        } catch (e) {
+          Cu.reportError("Could not sample scrollbar size: " + e + " -- " +
+                         e.stack);
+          sbWidth.value = 0;
+        }
+        // Minimum width of 10 so that we have enough padding:
+        sbWidth.value = Math.max(sbWidth.value, 10);
+        resolve(sbWidth.value);
+        iframe.remove();
+      });
+    });
+  }
+};
+Object.freeze(this.ScrollbarSampler);
diff --git a/application/basilisk/components/customizableui/content/customizeMode.inc.xul b/application/basilisk/components/customizableui/content/customizeMode.inc.xul
new file mode 100644
index 000000000..b665630a2
--- /dev/null
+++ b/application/basilisk/components/customizableui/content/customizeMode.inc.xul
@@ -0,0 +1,82 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<hbox id="customization-container" flex="1" hidden="true">
+  <vbox flex="1" id="customization-palette-container">
+    <label id="customization-header">
+      &customizeMode.menuAndToolbars.header2;
+    </label>
+    <hbox id="customization-empty" hidden="true">
+      <label>&customizeMode.menuAndToolbars.empty;</label>
+      <label onclick="BrowserOpenAddonsMgr('addons://discover/');"
+             onkeypress="BrowserOpenAddonsMgr('addons://discover/');"
+             id="customization-more-tools"
+             class="text-link">
+        &customizeMode.menuAndToolbars.emptyLink;
+      </label>
+    </hbox>
+    <vbox id="customization-palette" class="customization-palette"/>
+    <spacer id="customization-spacer"/>
+    <hbox id="customization-footer">
+#ifdef CAN_DRAW_IN_TITLEBAR
+      <button id="customization-titlebar-visibility-button" class="customizationmode-button"
+              label="&customizeMode.titlebar;" type="checkbox"
+#NB: because oncommand fires after click, by the time we've fired, the checkbox binding
+#    will already have switched the button's state, so this is correct:
+              oncommand="gCustomizeMode.toggleTitlebar(this.hasAttribute('checked'))"/>
+#endif
+      <button id="customization-toolbar-visibility-button" label="&customizeMode.toolbars;" class="customizationmode-button" type="menu">
+        <menupopup id="customization-toolbar-menu" onpopupshowing="onViewToolbarsPopupShowing(event)"/>
+      </button>
+      <button id="customization-lwtheme-button" label="&customizeMode.lwthemes;" class="customizationmode-button" type="menu">
+        <panel type="arrow" id="customization-lwtheme-menu"
+               onpopupshowing="gCustomizeMode.onLWThemesMenuShowing(event);"
+               position="topcenter bottomleft"
+               flip="none"
+               role="menu">
+          <label id="customization-lwtheme-menu-header" value="&customizeMode.lwthemes.myThemes;"/>
+          <label id="customization-lwtheme-menu-recommended" value="&customizeMode.lwthemes.recommended;"/>
+          <hbox id="customization-lwtheme-menu-footer">
+            <toolbarbutton class="customization-lwtheme-menu-footeritem"
+                           label="&customizeMode.lwthemes.menuManage;"
+                           accesskey="&customizeMode.lwthemes.menuManage.accessKey;"
+                           tabindex="0"
+                           oncommand="gCustomizeMode.openAddonsManagerThemes(event);"/>
+            <toolbarbutton class="customization-lwtheme-menu-footeritem"
+                           label="&customizeMode.lwthemes.menuGetMore;"
+                           accesskey="&customizeMode.lwthemes.menuGetMore.accessKey;"
+                           tabindex="0"
+                           oncommand="gCustomizeMode.getMoreThemes(event);"/>
+          </hbox>
+        </panel>
+      </button>
+
+      <spacer id="customization-footer-spacer"/>
+      <button id="customization-undo-reset-button"
+              class="customizationmode-button"
+              hidden="true"
+              oncommand="gCustomizeMode.undoReset();"
+              label="&undoCmd.label;"/>
+      <button id="customization-reset-button"
+              oncommand="gCustomizeMode.reset();"
+              label="&customizeMode.restoreDefaults;"
+              class="customizationmode-button"/>
+    </hbox>
+  </vbox>
+  <vbox id="customization-panel-container">
+    <vbox id="customization-panelWrapper">
+      <html:style html:type="text/html" scoped="scoped">
+        @import url(chrome://global/skin/popup.css);
+      </html:style>
+      <box class="panel-arrowbox">
+        <box flex="1"/>
+        <image class="panel-arrow" side="top"/>
+      </box>
+      <box class="panel-arrowcontent" side="top" flex="1">
+        <hbox id="customization-panelHolder"/>
+        <box class="panel-inner-arrowcontentfooter" hidden="true"/>
+      </box>
+    </vbox>
+  </vbox>
+</hbox>
diff --git a/application/basilisk/components/customizableui/content/jar.mn b/application/basilisk/components/customizableui/content/jar.mn
new file mode 100644
index 000000000..4efefd37d
--- /dev/null
+++ b/application/basilisk/components/customizableui/content/jar.mn
@@ -0,0 +1,10 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+browser.jar:
+  content/browser/customizableui/panelUI.css
+* content/browser/customizableui/panelUI.js
+  content/browser/customizableui/panelUI.xml
+  content/browser/customizableui/toolbar.xml
+
diff --git a/application/basilisk/components/customizableui/content/moz.build b/application/basilisk/components/customizableui/content/moz.build
new file mode 100644
index 000000000..eb4454d28
--- /dev/null
+++ b/application/basilisk/components/customizableui/content/moz.build
@@ -0,0 +1,7 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+JAR_MANIFESTS += ['jar.mn']
\ No newline at end of file
diff --git a/application/basilisk/components/customizableui/content/panelUI.css b/application/basilisk/components/customizableui/content/panelUI.css
new file mode 100644
index 000000000..ba44636f1
--- /dev/null
+++ b/application/basilisk/components/customizableui/content/panelUI.css
@@ -0,0 +1,31 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+.panel-viewstack[viewtype="main"] > .panel-clickcapturer {
+  pointer-events: none;
+}
+
+.panel-mainview,
+.panel-viewcontainer,
+.panel-viewstack {
+  overflow: hidden;
+}
+
+.panel-viewstack {
+  position: relative;
+}
+
+.panel-subviews {
+  -moz-stack-sizing: ignore;
+  transform: translateX(0);
+  overflow-y: auto;
+}
+
+.panel-subviews[panelopen] {
+  transition: transform var(--panelui-subview-transition-duration);
+}
+
+.panel-viewcontainer[panelopen]:-moz-any(:not([viewtype="main"]),[transitioning="true"]) {
+  transition: height var(--panelui-subview-transition-duration);
+}
diff --git a/application/basilisk/components/customizableui/content/panelUI.inc.xul b/application/basilisk/components/customizableui/content/panelUI.inc.xul
new file mode 100644
index 000000000..0ba9bc564
--- /dev/null
+++ b/application/basilisk/components/customizableui/content/panelUI.inc.xul
@@ -0,0 +1,406 @@
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<panel id="PanelUI-popup"
+       role="group"
+       type="arrow"
+       hidden="true"
+       flip="slide"
+       position="bottomcenter topright"
+       noautofocus="true">
+  <panelmultiview id="PanelUI-multiView" mainViewId="PanelUI-mainView">
+    <panelview id="PanelUI-mainView" context="customizationPanelContextMenu">
+      <vbox id="PanelUI-contents-scroller">
+        <vbox id="PanelUI-contents" class="panelUI-grid"/>
+      </vbox>
+
+      <footer id="PanelUI-footer">
+        <vbox id="PanelUI-footer-addons"></vbox>
+        <toolbarbutton id="PanelUI-update-status"
+                       oncommand="gMenuButtonUpdateBadge.onMenuPanelCommand(event);"
+                       wrap="true"
+                       hidden="true"/>
+        <hbox id="PanelUI-footer-fxa">
+          <hbox id="PanelUI-fxa-status"
+                defaultlabel="&fxaSignIn.label;"
+                signedinTooltiptext="&fxaSignedIn.tooltip;"
+                tooltiptext="&fxaSignedIn.tooltip;"
+                errorlabel="&fxaSignInError.label;"
+                unverifiedlabel="&fxaUnverified.label;"
+                onclick="if (event.which == 1) gFxAccounts.onMenuPanelCommand();">
+            <image id="PanelUI-fxa-avatar"/>
+            <toolbarbutton id="PanelUI-fxa-label"
+                           fxabrandname="&syncBrand.fxAccount.label;"/>
+          </hbox>
+          <toolbarseparator/>
+          <toolbarbutton id="PanelUI-fxa-icon"
+                         oncommand="gSyncUI.doSync();"
+                         closemenu="none">
+            <observes element="sync-status" attribute="syncstatus"/>
+            <observes element="sync-status" attribute="tooltiptext"/>
+          </toolbarbutton>
+        </hbox>
+
+        <hbox id="PanelUI-footer-inner">
+          <toolbarbutton id="PanelUI-customize" label="&appMenuCustomize.label;"
+                         exitLabel="&appMenuCustomizeExit.label;"
+                         tooltiptext="&appMenuCustomize.tooltip;"
+                         exitTooltiptext="&appMenuCustomizeExit.tooltip;"
+                         closemenu="none"
+                         oncommand="gCustomizeMode.toggle();"/>
+          <toolbarseparator/>
+          <toolbarbutton id="PanelUI-help" label="&helpMenu.label;"
+                         closemenu="none"
+                         tooltiptext="&appMenuHelp.tooltip;"
+                         oncommand="PanelUI.showHelpView(this);"/>
+          <toolbarseparator/>
+          <toolbarbutton id="PanelUI-quit"
+#ifdef XP_WIN
+                         label="&quitApplicationCmdWin2.label;"
+                         tooltiptext="&quitApplicationCmdWin2.tooltip;"
+#else
+#ifdef XP_MACOSX
+                         label="&quitApplicationCmdMac2.label;"
+#else
+                         label="&quitApplicationCmd.label;"
+#endif
+#endif
+                         command="cmd_quitApplication"/>
+        </hbox>
+      </footer>
+    </panelview>
+
+    <panelview id="PanelUI-history" flex="1">
+      <label value="&appMenuHistory.label;" class="panel-subview-header"/>
+      <vbox class="panel-subview-body">
+        <toolbarbutton id="appMenuViewHistorySidebar"
+                       label="&appMenuHistory.viewSidebar.label;"
+                       type="checkbox"
+                       class="subviewbutton"
+                       key="key_gotoHistory"
+                       oncommand="SidebarUI.toggle('viewHistorySidebar'); PanelUI.hide();">
+          <observes element="viewHistorySidebar" attribute="checked"/>
+        </toolbarbutton>
+        <toolbarbutton id="appMenuClearRecentHistory"
+                       label="&appMenuHistory.clearRecent.label;"
+                       class="subviewbutton"
+                       command="Tools:Sanitize"/>
+        <toolbarbutton id="appMenuRestoreLastSession"
+                       label="&appMenuHistory.restoreSession.label;"
+                       class="subviewbutton"
+                       command="Browser:RestoreLastSession"/>
+        <menuseparator id="PanelUI-recentlyClosedTabs-separator"/>
+        <vbox id="PanelUI-recentlyClosedTabs" tooltip="bhTooltip"/>
+        <menuseparator id="PanelUI-recentlyClosedWindows-separator"/>
+        <vbox id="PanelUI-recentlyClosedWindows" tooltip="bhTooltip"/>
+        <menuseparator id="PanelUI-historyItems-separator"/>
+        <vbox id="PanelUI-historyItems" tooltip="bhTooltip"/>
+      </vbox>
+      <toolbarbutton id="PanelUI-historyMore"
+                     class="panel-subview-footer subviewbutton"
+                     label="&appMenuHistory.showAll.label;"
+                     oncommand="PlacesCommandHook.showPlacesOrganizer('History'); CustomizableUI.hidePanelForNode(this);"/>
+    </panelview>
+
+    <panelview id="PanelUI-remotetabs" flex="1" class="PanelUI-subView">
+      <label value="&appMenuRemoteTabs.label;" class="panel-subview-header"/>
+      <vbox class="panel-subview-body">
+        <!-- this widget has 3 boxes in the body, but only 1 is ever visible -->
+        <!-- When Sync is ready to sync -->
+        <vbox id="PanelUI-remotetabs-main" observes="sync-syncnow-state">
+          <vbox id="PanelUI-remotetabs-buttons">
+            <toolbarbutton id="PanelUI-remotetabs-view-sidebar"
+                           class="subviewbutton"
+                           observes="viewTabsSidebar"
+                           label="&appMenuRemoteTabs.sidebar.label;"/>
+            <toolbarbutton id="PanelUI-remotetabs-syncnow"
+                           observes="sync-status"
+                           class="subviewbutton"
+                           oncommand="gSyncUI.doSync();"
+                           closemenu="none"/>
+            <menuseparator id="PanelUI-remotetabs-separator"/>
+          </vbox>
+          <deck id="PanelUI-remotetabs-deck">
+            <!-- Sync is ready to Sync and the "tabs" engine is enabled -->
+            <vbox id="PanelUI-remotetabs-tabspane">
+              <vbox id="PanelUI-remotetabs-tabslist"
+                    notabsforclientlabel="&appMenuRemoteTabs.notabs.label;"
+                    />
+            </vbox>
+            <!-- Sync is ready to Sync but the "tabs" engine isn't enabled-->
+            <hbox id="PanelUI-remotetabs-tabsdisabledpane" pack="center" flex="1">
+              <vbox class="PanelUI-remotetabs-instruction-box">
+                <hbox pack="center">
+                  <image class="fxaSyncIllustration" alt=""/>
+                </hbox>
+                <label class="PanelUI-remotetabs-instruction-label">&appMenuRemoteTabs.tabsnotsyncing.label;</label>
+                <hbox pack="center">
+                  <toolbarbutton class="PanelUI-remotetabs-prefs-button"
+                                 label="&appMenuRemoteTabs.openprefs.label;"
+                                 oncommand="gSyncUI.openSetup(null, 'synced-tabs');"/>
+                </hbox>
+              </vbox>
+            </hbox>
+            <!-- Sync is ready to Sync but we are still fetching the tabs to show -->
+            <vbox id="PanelUI-remotetabs-fetching">
+              <!-- Show intentionally blank panel, see bug 1239845 -->
+            </vbox>
+            <!-- Sync has only 1 (ie, this) device connected -->
+            <hbox id="PanelUI-remotetabs-nodevicespane" pack="center" flex="1">
+              <vbox class="PanelUI-remotetabs-instruction-box">
+                <hbox pack="center">
+                  <image class="fxaSyncIllustration" alt=""/>
+                </hbox>
+                <label class="PanelUI-remotetabs-instruction-title">&appMenuRemoteTabs.noclients.title;</label>
+                <label class="PanelUI-remotetabs-instruction-label">&appMenuRemoteTabs.noclients.subtitle;</label>
+                <!-- The inner HTML for PanelUI-remotetabs-mobile-promo is built at runtime -->
+                <label id="PanelUI-remotetabs-mobile-promo" fxAccountsBrand="&syncBrand.fxAccount.label;"/>
+              </vbox>
+            </hbox>
+          </deck>
+        </vbox>
+        <!-- a box to ensure contained boxes are centered horizonally -->
+        <hbox pack="center" flex="1">
+          <!-- When Sync is not configured -->
+          <vbox id="PanelUI-remotetabs-setupsync"
+                flex="1"
+                align="center"
+                class="PanelUI-remotetabs-instruction-box"
+                observes="sync-setup-state">
+            <image class="fxaSyncIllustration" alt=""/>
+            <label class="PanelUI-remotetabs-instruction-label">&appMenuRemoteTabs.notsignedin.label;</label>
+            <toolbarbutton class="PanelUI-remotetabs-prefs-button"
+                           label="&appMenuRemoteTabs.signin.label;"
+                           oncommand="gSyncUI.openSetup(null, 'synced-tabs');"/>
+          </vbox>
+          <!-- When Sync needs re-authentication. This uses the exact same messaging
+               as "Sync is not configured" but remains a separate box so we get
+               the goodness of observing broadcasters to manage the hidden states -->
+          <vbox id="PanelUI-remotetabs-reauthsync"
+                flex="1"
+                align="center"
+                class="PanelUI-remotetabs-instruction-box"
+                observes="sync-reauth-state">
+            <image class="fxaSyncIllustration" alt=""/>
+            <label class="PanelUI-remotetabs-instruction-label">&appMenuRemoteTabs.notsignedin.label;</label>
+            <toolbarbutton class="PanelUI-remotetabs-prefs-button"
+                           label="&appMenuRemoteTabs.signin.label;"
+                           oncommand="gSyncUI.openSetup(null, 'synced-tabs');"/>
+          </vbox>
+        </hbox>
+      </vbox>
+    </panelview>
+
+    <panelview id="PanelUI-bookmarks" flex="1" class="PanelUI-subView">
+      <label value="&bookmarksMenu.label;" class="panel-subview-header"/>
+      <vbox class="panel-subview-body">
+        <toolbarbutton id="panelMenuBookmarkThisPage"
+                       class="subviewbutton"
+                       observes="bookmarkThisPageBroadcaster"
+                       command="Browser:AddBookmarkAs"
+                       onclick="PanelUI.hide();"/>
+        <toolbarseparator/>
+        <toolbarbutton id="panelMenu_viewBookmarksSidebar"
+                       label="&viewBookmarksSidebar2.label;"
+                       class="subviewbutton"
+                       key="viewBookmarksSidebarKb"
+                       oncommand="SidebarUI.toggle('viewBookmarksSidebar'); PanelUI.hide();">
+          <observes element="viewBookmarksSidebar" attribute="checked"/>
+        </toolbarbutton>
+        <toolbarbutton id="panelMenu_viewBookmarksToolbar"
+                       label="&viewBookmarksToolbar.label;"
+                       type="checkbox"
+                       toolbarId="PersonalToolbar"
+                       class="subviewbutton"
+                       oncommand="onViewToolbarCommand(event); PanelUI.hide();"/>
+        <toolbarseparator/>
+        <toolbarbutton id="panelMenu_bookmarksToolbar"
+                       label="&personalbarCmd.label;"
+                       class="subviewbutton cui-withicon"
+                       oncommand="PlacesCommandHook.showPlacesOrganizer('BookmarksToolbar'); PanelUI.hide();"/>
+        <toolbarbutton id="panelMenu_unsortedBookmarks"
+                       label="&otherBookmarksCmd.label;"
+                       class="subviewbutton cui-withicon"
+                       oncommand="PlacesCommandHook.showPlacesOrganizer('UnfiledBookmarks'); PanelUI.hide();"/>
+        <toolbarseparator class="small-separator"/>
+        <toolbaritem id="panelMenu_bookmarksMenu"
+                     orient="vertical"
+                     smoothscroll="false"
+                     onclick="if (event.button == 1) BookmarkingUI.onPanelMenuViewCommand(event, this._placesView);"
+                     oncommand="BookmarkingUI.onPanelMenuViewCommand(event, this._placesView);"
+                     flatList="true"
+                     tooltip="bhTooltip">
+          <!-- bookmarks menu items will go here -->
+        </toolbaritem>
+      </vbox>
+      <toolbarbutton id="panelMenu_showAllBookmarks"
+                     label="&showAllBookmarks2.label;"
+                     class="subviewbutton panel-subview-footer"
+                     command="Browser:ShowAllBookmarks"
+                     onclick="PanelUI.hide();"/>
+    </panelview>
+
+    <panelview id="PanelUI-feeds" flex="1" oncommand="FeedHandler.subscribeToFeed(null, event);">
+      <label value="&feedsMenu2.label;" class="panel-subview-header"/>
+    </panelview>
+
+    <panelview id="PanelUI-containers" flex="1">
+      <label value="&containersMenu.label;" class="panel-subview-header"/>
+      <vbox id="PanelUI-containersItems"/>
+    </panelview>
+
+    <panelview id="PanelUI-helpView" flex="1" class="PanelUI-subView">
+      <label value="&helpMenu.label;" class="panel-subview-header"/>
+      <vbox id="PanelUI-helpItems" class="panel-subview-body"/>
+    </panelview>
+
+    <panelview id="PanelUI-developer" flex="1">
+      <label value="&webDeveloperMenu.label;" class="panel-subview-header"/>
+      <vbox id="PanelUI-developerItems" class="panel-subview-body"/>
+    </panelview>
+
+    <panelview id="PanelUI-sidebar" flex="1">
+      <label value="&appMenuSidebars.label;" class="panel-subview-header"/>
+      <vbox id="PanelUI-sidebarItems" class="panel-subview-body"/>
+    </panelview>
+
+    <panelview id="PanelUI-characterEncodingView" flex="1">
+      <label value="&charsetMenu2.label;" class="panel-subview-header"/>
+      <vbox class="panel-subview-body">
+        <vbox id="PanelUI-characterEncodingView-pinned"
+              class="PanelUI-characterEncodingView-list"/>
+        <toolbarseparator/>
+        <vbox id="PanelUI-characterEncodingView-charsets"
+              class="PanelUI-characterEncodingView-list"/>
+        <toolbarseparator/>
+        <vbox>
+          <label id="PanelUI-characterEncodingView-autodetect-label"/>
+          <vbox id="PanelUI-characterEncodingView-autodetect"
+                class="PanelUI-characterEncodingView-list"/>
+        </vbox>
+      </vbox>
+    </panelview>
+
+    <panelview id="PanelUI-panicView" flex="1">
+      <vbox class="panel-subview-body">
+        <hbox id="PanelUI-panic-timeframe">
+          <image id="PanelUI-panic-timeframe-icon" alt=""/>
+          <vbox flex="1">
+            <hbox id="PanelUI-panic-header">
+              <image id="PanelUI-panic-timeframe-icon-small" alt=""/>
+              <description id="PanelUI-panic-mainDesc" flex="1">&panicButton.view.mainTimeframeDesc;</description>
+            </hbox>
+            <radiogroup id="PanelUI-panic-timeSpan" aria-labelledby="PanelUI-panic-mainDesc" closemenu="none">
+              <radio id="PanelUI-panic-5min" label="&panicButton.view.5min;" selected="true"
+                     value="5" class="subviewradio"/>
+              <radio id="PanelUI-panic-2hr" label="&panicButton.view.2hr;"
+                     value="2" class="subviewradio"/>
+              <radio id="PanelUI-panic-day" label="&panicButton.view.day;"
+                     value="6" class="subviewradio"/>
+            </radiogroup>
+          </vbox>
+        </hbox>
+        <vbox id="PanelUI-panic-explanations">
+          <label id="PanelUI-panic-actionlist-main-label">&panicButton.view.mainActionDesc;</label>
+
+          <label id="PanelUI-panic-actionlist-windows" class="PanelUI-panic-actionlist">&panicButton.view.deleteTabsAndWindows;</label>
+          <label id="PanelUI-panic-actionlist-cookies" class="PanelUI-panic-actionlist">&panicButton.view.deleteCookies;</label>
+          <label id="PanelUI-panic-actionlist-history" class="PanelUI-panic-actionlist">&panicButton.view.deleteHistory;</label>
+          <label id="PanelUI-panic-actionlist-newwindow" class="PanelUI-panic-actionlist">&panicButton.view.openNewWindow;</label>
+
+          <label id="PanelUI-panic-warning">&panicButton.view.undoWarning;</label>
+        </vbox>
+        <button id="PanelUI-panic-view-button"
+                label="&panicButton.view.forgetButton;"/>
+      </vbox>
+    </panelview>
+
+  </panelmultiview>
+  <!-- These menupopups are located here to prevent flickering,
+       see bug 492960 comment 20. -->
+  <menupopup id="customizationPanelItemContextMenu">
+    <menuitem oncommand="gCustomizeMode.addToToolbar(document.popupNode)"
+              closemenu="single"
+              class="customize-context-moveToToolbar"
+              accesskey="&customizeMenu.moveToToolbar.accesskey;"
+              label="&customizeMenu.moveToToolbar.label;"/>
+    <menuitem oncommand="gCustomizeMode.removeFromArea(document.popupNode)"
+              closemenu="single"
+              class="customize-context-removeFromPanel"
+              accesskey="&customizeMenu.removeFromMenu.accesskey;"
+              label="&customizeMenu.removeFromMenu.label;"/>
+    <menuseparator/>
+    <menuitem command="cmd_CustomizeToolbars"
+              class="viewCustomizeToolbar"
+              accesskey="&viewCustomizeToolbar.accesskey;"
+              label="&viewCustomizeToolbar.label;"/>
+  </menupopup>
+
+  <menupopup id="customizationPaletteItemContextMenu">
+    <menuitem oncommand="gCustomizeMode.addToToolbar(document.popupNode)"
+              class="customize-context-addToToolbar"
+              accesskey="&customizeMenu.addToToolbar.accesskey;"
+              label="&customizeMenu.addToToolbar.label;"/>
+    <menuitem oncommand="gCustomizeMode.addToPanel(document.popupNode)"
+              class="customize-context-addToPanel"
+              accesskey="&customizeMenu.addToPanel.accesskey;"
+              label="&customizeMenu.addToPanel.label;"/>
+  </menupopup>
+
+  <menupopup id="customizationPanelContextMenu">
+    <menuitem command="cmd_CustomizeToolbars"
+              accesskey="&customizeMenu.addMoreItems.accesskey;"
+              label="&customizeMenu.addMoreItems.label;"/>
+  </menupopup>
+</panel>
+
+<panel id="widget-overflow"
+       role="group"
+       type="arrow"
+       noautofocus="true"
+       context="toolbar-context-menu"
+       position="bottomcenter topright"
+       hidden="true">
+  <vbox id="widget-overflow-scroller">
+    <vbox id="widget-overflow-list" class="widget-overflow-list"
+          overflowfortoolbar="nav-bar"/>
+  </vbox>
+</panel>
+
+<panel id="customization-tipPanel"
+       type="arrow"
+       flip="none"
+       side="left"
+       position="leftcenter topright"
+       noautohide="true"
+       hidden="true">
+  <hbox class="customization-tipPanel-wrapper">
+    <vbox class="customization-tipPanel-infoBox"/>
+    <vbox class="customization-tipPanel-content" flex="1">
+      <description class="customization-tipPanel-contentMessage"/>
+      <image class="customization-tipPanel-contentImage"/>
+    </vbox>
+    <vbox pack="start" align="end" class="customization-tipPanel-closeBox">
+      <toolbarbutton oncommand="gCustomizeMode.hideTip()" class="close-icon"/>
+    </vbox>
+  </hbox>
+</panel>
+
+<panel id="panic-button-success-notification"
+       type="arrow"
+       position="bottomcenter topright"
+       hidden="true"
+       role="alert"
+       orient="vertical">
+  <hbox id="panic-button-success-header">
+    <image id="panic-button-success-icon" alt=""/>
+    <vbox>
+      <description>&panicButton.thankyou.msg1;</description>
+      <description>&panicButton.thankyou.msg2;</description>
+    </vbox>
+  </hbox>
+  <button label="&panicButton.thankyou.buttonlabel;"
+          id="panic-button-success-closebutton"
+          oncommand="PanicButtonNotifier.close()"/>
+</panel>
diff --git a/application/basilisk/components/customizableui/content/panelUI.js b/application/basilisk/components/customizableui/content/panelUI.js
new file mode 100644
index 000000000..13f8ade2b
--- /dev/null
+++ b/application/basilisk/components/customizableui/content/panelUI.js
@@ -0,0 +1,558 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+XPCOMUtils.defineLazyModuleGetter(this, "CustomizableUI",
+                                  "resource:///modules/CustomizableUI.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "ScrollbarSampler",
+                                  "resource:///modules/ScrollbarSampler.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "ShortcutUtils",
+                                  "resource://gre/modules/ShortcutUtils.jsm");
+
+/**
+ * Maintains the state and dispatches events for the main menu panel.
+ */
+
+const PanelUI = {
+  /** Panel events that we listen for. **/
+  get kEvents() {
+    return ["popupshowing", "popupshown", "popuphiding", "popuphidden"];
+  },
+  /**
+   * Used for lazily getting and memoizing elements from the document. Lazy
+   * getters are set in init, and memoizing happens after the first retrieval.
+   */
+  get kElements() {
+    return {
+      contents: "PanelUI-contents",
+      mainView: "PanelUI-mainView",
+      multiView: "PanelUI-multiView",
+      helpView: "PanelUI-helpView",
+      menuButton: "PanelUI-menu-button",
+      panel: "PanelUI-popup",
+      scroller: "PanelUI-contents-scroller"
+    };
+  },
+
+  _initialized: false,
+  init() {
+    for (let [k, v] of Object.entries(this.kElements)) {
+      // Need to do fresh let-bindings per iteration
+      let getKey = k;
+      let id = v;
+      this.__defineGetter__(getKey, function() {
+        delete this[getKey];
+        return this[getKey] = document.getElementById(id);
+      });
+    }
+
+    this.menuButton.addEventListener("mousedown", this);
+    this.menuButton.addEventListener("keypress", this);
+    this._overlayScrollListenerBoundFn = this._overlayScrollListener.bind(this);
+    window.matchMedia("(-moz-overlay-scrollbars)").addListener(this._overlayScrollListenerBoundFn);
+    CustomizableUI.addListener(this);
+    this._initialized = true;
+  },
+
+  _eventListenersAdded: false,
+  _ensureEventListenersAdded() {
+    if (this._eventListenersAdded)
+      return;
+    this._addEventListeners();
+  },
+
+  _addEventListeners() {
+    for (let event of this.kEvents) {
+      this.panel.addEventListener(event, this);
+    }
+
+    this.helpView.addEventListener("ViewShowing", this._onHelpViewShow);
+    this._eventListenersAdded = true;
+  },
+
+  uninit() {
+    for (let event of this.kEvents) {
+      this.panel.removeEventListener(event, this);
+    }
+    this.helpView.removeEventListener("ViewShowing", this._onHelpViewShow);
+    this.menuButton.removeEventListener("mousedown", this);
+    this.menuButton.removeEventListener("keypress", this);
+    window.matchMedia("(-moz-overlay-scrollbars)").removeListener(this._overlayScrollListenerBoundFn);
+    CustomizableUI.removeListener(this);
+    this._overlayScrollListenerBoundFn = null;
+  },
+
+  /**
+   * Customize mode extracts the mainView and puts it somewhere else while the
+   * user customizes. Upon completion, this function can be called to put the
+   * panel back to where it belongs in normal browsing mode.
+   *
+   * @param aMainView
+   *        The mainView node to put back into place.
+   */
+  setMainView(aMainView) {
+    this._ensureEventListenersAdded();
+    this.multiView.setMainView(aMainView);
+  },
+
+  /**
+   * Opens the menu panel if it's closed, or closes it if it's
+   * open.
+   *
+   * @param aEvent the event that triggers the toggle.
+   */
+  toggle(aEvent) {
+    // Don't show the panel if the window is in customization mode,
+    // since this button doubles as an exit path for the user in this case.
+    if (document.documentElement.hasAttribute("customizing")) {
+      return;
+    }
+    this._ensureEventListenersAdded();
+    if (this.panel.state == "open") {
+      this.hide();
+    } else if (this.panel.state == "closed") {
+      this.show(aEvent);
+    }
+  },
+
+  /**
+   * Opens the menu panel. If the event target has a child with the
+   * toolbarbutton-icon attribute, the panel will be anchored on that child.
+   * Otherwise, the panel is anchored on the event target itself.
+   *
+   * @param aEvent the event (if any) that triggers showing the menu.
+   */
+  show(aEvent) {
+    return new Promise(resolve => {
+      this.ensureReady().then(() => {
+        if (this.panel.state == "open" ||
+            document.documentElement.hasAttribute("customizing")) {
+          resolve();
+          return;
+        }
+
+        let editControlPlacement = CustomizableUI.getPlacementOfWidget("edit-controls");
+        if (editControlPlacement && editControlPlacement.area == CustomizableUI.AREA_PANEL) {
+          updateEditUIVisibility();
+        }
+
+        let personalBookmarksPlacement = CustomizableUI.getPlacementOfWidget("personal-bookmarks");
+        if (personalBookmarksPlacement &&
+            personalBookmarksPlacement.area == CustomizableUI.AREA_PANEL) {
+          PlacesToolbarHelper.customizeChange();
+        }
+
+        let anchor;
+        if (!aEvent ||
+            aEvent.type == "command") {
+          anchor = this.menuButton;
+        } else {
+          anchor = aEvent.target;
+        }
+
+        this.panel.addEventListener("popupshown", function onPopupShown() {
+          this.removeEventListener("popupshown", onPopupShown);
+          resolve();
+        });
+
+        let iconAnchor =
+          document.getAnonymousElementByAttribute(anchor, "class",
+                                                  "toolbarbutton-icon");
+        this.panel.openPopup(iconAnchor || anchor);
+      }, (reason) => {
+        console.error("Error showing the PanelUI menu", reason);
+      });
+    });
+  },
+
+  /**
+   * If the menu panel is being shown, hide it.
+   */
+  hide() {
+    if (document.documentElement.hasAttribute("customizing")) {
+      return;
+    }
+
+    this.panel.hidePopup();
+  },
+
+  handleEvent(aEvent) {
+    // Ignore context menus and menu button menus showing and hiding:
+    if (aEvent.type.startsWith("popup") &&
+        aEvent.target != this.panel) {
+      return;
+    }
+    switch (aEvent.type) {
+      case "popupshowing":
+        this._adjustLabelsForAutoHyphens();
+        // Fall through
+      case "popupshown":
+        // Fall through
+      case "popuphiding":
+        // Fall through
+      case "popuphidden":
+        this._updatePanelButton(aEvent.target);
+        break;
+      case "mousedown":
+        if (aEvent.button == 0)
+          this.toggle(aEvent);
+        break;
+      case "keypress":
+        this.toggle(aEvent);
+        break;
+    }
+  },
+
+  get isReady() {
+    return !!this._isReady;
+  },
+
+  /**
+   * Registering the menu panel is done lazily for performance reasons. This
+   * method is exposed so that CustomizationMode can force panel-readyness in the
+   * event that customization mode is started before the panel has been opened
+   * by the user.
+   *
+   * @param aCustomizing (optional) set to true if this was called while entering
+   *        customization mode. If that's the case, we trust that customization
+   *        mode will handle calling beginBatchUpdate and endBatchUpdate.
+   *
+   * @return a Promise that resolves once the panel is ready to roll.
+   */
+  ensureReady(aCustomizing = false) {
+    if (this._readyPromise) {
+      return this._readyPromise;
+    }
+    this._readyPromise = Task.spawn(function*() {
+      if (!this._initialized) {
+        yield new Promise(resolve => {
+          let delayedStartupObserver = (aSubject, aTopic, aData) => {
+            if (aSubject == window) {
+              Services.obs.removeObserver(delayedStartupObserver, "browser-delayed-startup-finished");
+              resolve();
+            }
+          };
+          Services.obs.addObserver(delayedStartupObserver, "browser-delayed-startup-finished", false);
+        });
+      }
+
+      this.contents.setAttributeNS("http://www.w3.org/XML/1998/namespace", "lang",
+                                   getLocale());
+      if (!this._scrollWidth) {
+        // In order to properly center the contents of the panel, while ensuring
+        // that we have enough space on either side to show a scrollbar, we have to
+        // do a bit of hackery. In particular, we calculate a new width for the
+        // scroller, based on the system scrollbar width.
+        this._scrollWidth =
+          (yield ScrollbarSampler.getSystemScrollbarWidth()) + "px";
+        let cstyle = window.getComputedStyle(this.scroller);
+        let widthStr = cstyle.width;
+        // Get the calculated padding on the left and right sides of
+        // the scroller too. We'll use that in our final calculation so
+        // that if a scrollbar appears, we don't have the contents right
+        // up against the edge of the scroller.
+        let paddingLeft = cstyle.paddingLeft;
+        let paddingRight = cstyle.paddingRight;
+        let calcStr = [widthStr, this._scrollWidth,
+                       paddingLeft, paddingRight].join(" + ");
+        this.scroller.style.width = "calc(" + calcStr + ")";
+      }
+
+      if (aCustomizing) {
+        CustomizableUI.registerMenuPanel(this.contents);
+      } else {
+        this.beginBatchUpdate();
+        try {
+          CustomizableUI.registerMenuPanel(this.contents);
+        } finally {
+          this.endBatchUpdate();
+        }
+      }
+      this._updateQuitTooltip();
+      this.panel.hidden = false;
+      this._isReady = true;
+    }.bind(this)).then(null, Cu.reportError);
+
+    return this._readyPromise;
+  },
+
+  /**
+   * Switch the panel to the main view if it's not already
+   * in that view.
+   */
+  showMainView() {
+    this._ensureEventListenersAdded();
+    this.multiView.showMainView();
+  },
+
+  /**
+   * Switch the panel to the help view if it's not already
+   * in that view.
+   */
+  showHelpView(aAnchor) {
+    this._ensureEventListenersAdded();
+    this.multiView.showSubView("PanelUI-helpView", aAnchor);
+  },
+
+  /**
+   * Shows a subview in the panel with a given ID.
+   *
+   * @param aViewId the ID of the subview to show.
+   * @param aAnchor the element that spawned the subview.
+   * @param aPlacementArea the CustomizableUI area that aAnchor is in.
+   */
+  showSubView: Task.async(function*(aViewId, aAnchor, aPlacementArea) {
+    this._ensureEventListenersAdded();
+    let viewNode = document.getElementById(aViewId);
+    if (!viewNode) {
+      Cu.reportError("Could not show panel subview with id: " + aViewId);
+      return;
+    }
+
+    if (!aAnchor) {
+      Cu.reportError("Expected an anchor when opening subview with id: " + aViewId);
+      return;
+    }
+
+    if (aPlacementArea == CustomizableUI.AREA_PANEL) {
+      this.multiView.showSubView(aViewId, aAnchor);
+    } else if (!aAnchor.open) {
+      aAnchor.open = true;
+
+      let tempPanel = document.createElement("panel");
+      tempPanel.setAttribute("type", "arrow");
+      tempPanel.setAttribute("id", "customizationui-widget-panel");
+      tempPanel.setAttribute("class", "cui-widget-panel");
+      tempPanel.setAttribute("viewId", aViewId);
+      if (aAnchor.getAttribute("tabspecific")) {
+        tempPanel.setAttribute("tabspecific", true);
+      }
+      if (this._disableAnimations) {
+        tempPanel.setAttribute("animate", "false");
+      }
+      tempPanel.setAttribute("context", "");
+      document.getElementById(CustomizableUI.AREA_NAVBAR).appendChild(tempPanel);
+      // If the view has a footer, set a convenience class on the panel.
+      tempPanel.classList.toggle("cui-widget-panelWithFooter",
+                                 viewNode.querySelector(".panel-subview-footer"));
+
+      let multiView = document.createElement("panelmultiview");
+      multiView.setAttribute("id", "customizationui-widget-multiview");
+      multiView.setAttribute("nosubviews", "true");
+      tempPanel.appendChild(multiView);
+      multiView.setAttribute("mainViewIsSubView", "true");
+      multiView.setMainView(viewNode);
+      viewNode.classList.add("cui-widget-panelview");
+
+      let viewShown = false;
+      let panelRemover = () => {
+        viewNode.classList.remove("cui-widget-panelview");
+        if (viewShown) {
+          CustomizableUI.removePanelCloseListeners(tempPanel);
+          tempPanel.removeEventListener("popuphidden", panelRemover);
+
+          let evt = new CustomEvent("ViewHiding", {detail: viewNode});
+          viewNode.dispatchEvent(evt);
+        }
+        aAnchor.open = false;
+
+        this.multiView.appendChild(viewNode);
+        tempPanel.remove();
+      };
+
+      // Emit the ViewShowing event so that the widget definition has a chance
+      // to lazily populate the subview with things.
+      let detail = {
+        blockers: new Set(),
+        addBlocker(aPromise) {
+          this.blockers.add(aPromise);
+        },
+      };
+
+      let evt = new CustomEvent("ViewShowing", { bubbles: true, cancelable: true, detail });
+      viewNode.dispatchEvent(evt);
+
+      let cancel = evt.defaultPrevented;
+      if (detail.blockers.size) {
+        try {
+          let results = yield Promise.all(detail.blockers);
+          cancel = cancel || results.some(val => val === false);
+        } catch (e) {
+          Components.utils.reportError(e);
+          cancel = true;
+        }
+      }
+
+      if (cancel) {
+        panelRemover();
+        return;
+      }
+
+      viewShown = true;
+      CustomizableUI.addPanelCloseListeners(tempPanel);
+      tempPanel.addEventListener("popuphidden", panelRemover);
+
+      let iconAnchor =
+        document.getAnonymousElementByAttribute(aAnchor, "class",
+                                                "toolbarbutton-icon");
+
+      if (iconAnchor && aAnchor.id) {
+        iconAnchor.setAttribute("consumeanchor", aAnchor.id);
+      }
+      tempPanel.openPopup(iconAnchor || aAnchor, "bottomcenter topright");
+    }
+  }),
+
+  /**
+   * NB: The enable- and disableSingleSubviewPanelAnimations methods only
+   * affect the hiding/showing animations of single-subview panels (tempPanel
+   * in the showSubView method).
+   */
+  disableSingleSubviewPanelAnimations() {
+    this._disableAnimations = true;
+  },
+
+  enableSingleSubviewPanelAnimations() {
+    this._disableAnimations = false;
+  },
+
+  onWidgetAfterDOMChange(aNode, aNextNode, aContainer, aWasRemoval) {
+    if (aContainer != this.contents) {
+      return;
+    }
+    if (aWasRemoval) {
+      aNode.removeAttribute("auto-hyphens");
+    }
+  },
+
+  onWidgetBeforeDOMChange(aNode, aNextNode, aContainer, aIsRemoval) {
+    if (aContainer != this.contents) {
+      return;
+    }
+    if (!aIsRemoval &&
+        (this.panel.state == "open" ||
+         document.documentElement.hasAttribute("customizing"))) {
+      this._adjustLabelsForAutoHyphens(aNode);
+    }
+  },
+
+  /**
+   * Signal that we're about to make a lot of changes to the contents of the
+   * panels all at once. For performance, we ignore the mutations.
+   */
+  beginBatchUpdate() {
+    this._ensureEventListenersAdded();
+    this.multiView.ignoreMutations = true;
+  },
+
+  /**
+   * Signal that we're done making bulk changes to the panel. We now pay
+   * attention to mutations. This automatically synchronizes the multiview
+   * container with whichever view is displayed if the panel is open.
+   */
+  endBatchUpdate(aReason) {
+    this._ensureEventListenersAdded();
+    this.multiView.ignoreMutations = false;
+  },
+
+  _adjustLabelsForAutoHyphens(aNode) {
+    let toolbarButtons = aNode ? [aNode] :
+                                 this.contents.querySelectorAll(".toolbarbutton-1");
+    for (let node of toolbarButtons) {
+      let label = node.getAttribute("label");
+      if (!label) {
+        continue;
+      }
+      if (label.includes("\u00ad")) {
+        node.setAttribute("auto-hyphens", "off");
+      } else {
+        node.removeAttribute("auto-hyphens");
+      }
+    }
+  },
+
+  /**
+   * Sets the anchor node into the open or closed state, depending
+   * on the state of the panel.
+   */
+  _updatePanelButton() {
+    this.menuButton.open = this.panel.state == "open" ||
+                           this.panel.state == "showing";
+  },
+
+  _onHelpViewShow(aEvent) {
+    // Call global menu setup function
+    buildHelpMenu();
+
+    let helpMenu = document.getElementById("menu_HelpPopup");
+    let items = this.getElementsByTagName("vbox")[0];
+    let attrs = ["oncommand", "onclick", "label", "key", "disabled"];
+    let NSXUL = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
+
+    // Remove all buttons from the view
+    while (items.firstChild) {
+      items.removeChild(items.firstChild);
+    }
+
+    // Add the current set of menuitems of the Help menu to this view
+    let menuItems = Array.prototype.slice.call(helpMenu.getElementsByTagName("menuitem"));
+    let fragment = document.createDocumentFragment();
+    for (let node of menuItems) {
+      if (node.hidden)
+        continue;
+      let button = document.createElementNS(NSXUL, "toolbarbutton");
+      // Copy specific attributes from a menuitem of the Help menu
+      for (let attrName of attrs) {
+        if (!node.hasAttribute(attrName))
+          continue;
+        button.setAttribute(attrName, node.getAttribute(attrName));
+      }
+      button.setAttribute("class", "subviewbutton");
+      fragment.appendChild(button);
+    }
+    items.appendChild(fragment);
+  },
+
+  _updateQuitTooltip() {
+#ifdef XP_WIN
+    return;
+#else
+#ifdef XP_MACOSX
+    let tooltipId = "quit-button.tooltiptext.mac"
+#else
+    let tooltipId = "quit-button.tooltiptext.linux2"
+#endif
+
+    let brands = Services.strings.createBundle("chrome://branding/locale/brand.properties");
+    let stringArgs = [brands.GetStringFromName("brandShortName")];
+
+    let key = document.getElementById("key_quitApplication");
+    stringArgs.push(ShortcutUtils.prettifyShortcut(key));
+    let tooltipString = CustomizableUI.getLocalizedProperty({x: tooltipId}, "x", stringArgs);
+    let quitButton = document.getElementById("PanelUI-quit");
+    quitButton.setAttribute("tooltiptext", tooltipString);
+#endif
+  },
+
+  _overlayScrollListenerBoundFn: null,
+  _overlayScrollListener(aMQL) {
+    ScrollbarSampler.resetSystemScrollbarWidth();
+    this._scrollWidth = null;
+  },
+};
+
+XPCOMUtils.defineConstant(this, "PanelUI", PanelUI);
+
+/**
+ * Gets the currently selected locale for display.
+ * @return  the selected locale or "en-US" if none is selected
+ */
+function getLocale() {
+  try {
+    let chromeRegistry = Cc["@mozilla.org/chrome/chrome-registry;1"]
+                           .getService(Ci.nsIXULChromeRegistry);
+    return chromeRegistry.getSelectedLocale("browser");
+  } catch (ex) {
+    return "en-US";
+  }
+}
diff --git a/application/basilisk/components/customizableui/content/panelUI.xml b/application/basilisk/components/customizableui/content/panelUI.xml
new file mode 100644
index 000000000..6893bd8ff
--- /dev/null
+++ b/application/basilisk/components/customizableui/content/panelUI.xml
@@ -0,0 +1,509 @@
+<?xml version="1.0"?>
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<bindings id="browserPanelUIBindings"
+          xmlns="http://www.mozilla.org/xbl"
+          xmlns:xul="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+          xmlns:xbl="http://www.mozilla.org/xbl">
+
+  <binding id="panelmultiview">
+    <resources>
+      <stylesheet src="chrome://browser/content/customizableui/panelUI.css"/>
+    </resources>
+    <content>
+      <xul:box anonid="viewContainer" class="panel-viewcontainer" xbl:inherits="panelopen,viewtype,transitioning">
+        <xul:stack anonid="viewStack" xbl:inherits="viewtype,transitioning" viewtype="main" class="panel-viewstack">
+          <xul:vbox anonid="mainViewContainer" class="panel-mainview" xbl:inherits="viewtype"/>
+
+          <!-- Used to capture click events over the PanelUI-mainView if we're in
+               subview mode. That way, any click on the PanelUI-mainView causes us
+               to revert to the mainView mode, whereupon PanelUI-click-capture then
+               allows click events to go through it. -->
+          <xul:vbox anonid="clickCapturer" class="panel-clickcapturer"/>
+
+          <!-- We manually set display: none (via a CSS attribute selector) on the
+               subviews that are not being displayed. We're using this over a deck
+               because a deck assumes the size of its largest child, regardless of
+               whether or not it is shown. That's not good for our case, since we
+               want to allow each subview to be uniquely sized. -->
+          <xul:vbox anonid="subViews" class="panel-subviews" xbl:inherits="panelopen">
+            <children includes="panelview"/>
+          </xul:vbox>
+        </xul:stack>
+      </xul:box>
+    </content>
+    <implementation implements="nsIDOMEventListener">
+      <field name="_clickCapturer" readonly="true">
+        document.getAnonymousElementByAttribute(this, "anonid", "clickCapturer");
+      </field>
+      <field name="_viewContainer" readonly="true">
+        document.getAnonymousElementByAttribute(this, "anonid", "viewContainer");
+      </field>
+      <field name="_mainViewContainer" readonly="true">
+        document.getAnonymousElementByAttribute(this, "anonid", "mainViewContainer");
+      </field>
+      <field name="_subViews" readonly="true">
+        document.getAnonymousElementByAttribute(this, "anonid", "subViews");
+      </field>
+      <field name="_viewStack" readonly="true">
+        document.getAnonymousElementByAttribute(this, "anonid", "viewStack");
+      </field>
+      <field name="_panel" readonly="true">
+        this.parentNode;
+      </field>
+
+      <field name="_currentSubView">null</field>
+      <field name="_anchorElement">null</field>
+      <field name="_mainViewHeight">0</field>
+      <field name="_subViewObserver">null</field>
+      <field name="__transitioning">false</field>
+      <field name="_ignoreMutations">false</field>
+
+      <property name="showingSubView" readonly="true"
+                onget="return this._viewStack.getAttribute('viewtype') == 'subview'"/>
+      <property name="_mainViewId" onget="return this.getAttribute('mainViewId');" onset="this.setAttribute('mainViewId', val); return val;"/>
+      <property name="_mainView" readonly="true"
+                onget="return this._mainViewId ? document.getElementById(this._mainViewId) : null;"/>
+      <property name="showingSubViewAsMainView" readonly="true"
+                onget="return this.getAttribute('mainViewIsSubView') == 'true'"/>
+
+      <property name="ignoreMutations">
+        <getter>
+          return this._ignoreMutations;
+        </getter>
+        <setter><![CDATA[
+          this._ignoreMutations = val;
+          if (!val && this._panel.state == "open") {
+            if (this.showingSubView) {
+              this._syncContainerWithSubView();
+            } else {
+              this._syncContainerWithMainView();
+            }
+          }
+        ]]></setter>
+      </property>
+
+      <property name="_transitioning">
+        <getter>
+          return this.__transitioning;
+        </getter>
+        <setter><![CDATA[
+          this.__transitioning = val;
+          if (val) {
+            this.setAttribute("transitioning", "true");
+          } else {
+            this.removeAttribute("transitioning");
+          }
+        ]]></setter>
+      </property>
+      <constructor><![CDATA[
+        this._clickCapturer.addEventListener("click", this);
+        this._panel.addEventListener("popupshowing", this);
+        this._panel.addEventListener("popupshown", this);
+        this._panel.addEventListener("popuphidden", this);
+        this._subViews.addEventListener("overflow", this);
+        this._mainViewContainer.addEventListener("overflow", this);
+
+        // Get a MutationObserver ready to react to subview size changes. We
+        // only attach this MutationObserver when a subview is being displayed.
+        this._subViewObserver =
+          new MutationObserver(this._syncContainerWithSubView.bind(this));
+        this._mainViewObserver =
+          new MutationObserver(this._syncContainerWithMainView.bind(this));
+
+        this._mainViewContainer.setAttribute("panelid",
+                                             this._panel.id);
+
+        if (this._mainView) {
+          this.setMainView(this._mainView);
+        }
+        this.setAttribute("viewtype", "main");
+      ]]></constructor>
+
+      <destructor><![CDATA[
+        if (this._mainView) {
+          this._mainView.removeAttribute("mainview");
+        }
+        this._mainViewObserver.disconnect();
+        this._subViewObserver.disconnect();
+        this._panel.removeEventListener("popupshowing", this);
+        this._panel.removeEventListener("popupshown", this);
+        this._panel.removeEventListener("popuphidden", this);
+        this._subViews.removeEventListener("overflow", this);
+        this._mainViewContainer.removeEventListener("overflow", this);
+        this._clickCapturer.removeEventListener("click", this);
+      ]]></destructor>
+
+      <method name="setMainView">
+        <parameter name="aNewMainView"/>
+        <body><![CDATA[
+        if (this._mainView) {
+          this._mainViewObserver.disconnect();
+          this._subViews.appendChild(this._mainView);
+          this._mainView.removeAttribute("mainview");
+        }
+        this._mainViewId = aNewMainView.id;
+        aNewMainView.setAttribute("mainview", "true");
+        this._mainViewContainer.appendChild(aNewMainView);
+        ]]></body>
+      </method>
+
+      <method name="showMainView">
+        <body><![CDATA[
+          if (this.showingSubView) {
+            let viewNode = this._currentSubView;
+            let evt = document.createEvent("CustomEvent");
+            evt.initCustomEvent("ViewHiding", true, true, viewNode);
+            viewNode.dispatchEvent(evt);
+
+            viewNode.removeAttribute("current");
+            this._currentSubView = null;
+
+            this._subViewObserver.disconnect();
+
+            this._setViewContainerHeight(this._mainViewHeight);
+
+            this.setAttribute("viewtype", "main");
+          }
+
+          this._shiftMainView();
+        ]]></body>
+      </method>
+
+      <method name="showSubView">
+        <parameter name="aViewId"/>
+        <parameter name="aAnchor"/>
+        <body><![CDATA[
+          Task.spawn(function*() {
+            let viewNode = this.querySelector("#" + aViewId);
+            viewNode.setAttribute("current", true);
+            // Emit the ViewShowing event so that the widget definition has a chance
+            // to lazily populate the subview with things.
+            let detail = {
+              blockers: new Set(),
+              addBlocker(aPromise) {
+                this.blockers.add(aPromise);
+              },
+            };
+
+            let evt = new CustomEvent("ViewShowing", { bubbles: true, cancelable: true, detail });
+            viewNode.dispatchEvent(evt);
+
+            let cancel = evt.defaultPrevented;
+            if (detail.blockers.size) {
+              try {
+                let results = yield Promise.all(detail.blockers);
+                cancel = cancel || results.some(val => val === false);
+              } catch (e) {
+                Components.utils.reportError(e);
+                cancel = true;
+              }
+            }
+
+            if (cancel) {
+              return;
+            }
+
+            this._currentSubView = viewNode;
+
+            // Now we have to transition the panel. There are a few parts to this:
+            //
+            // 1) The main view content gets shifted so that the center of the anchor
+            //    node is at the left-most edge of the panel.
+            // 2) The subview deck slides in so that it takes up almost all of the
+            //    panel.
+            // 3) If the subview is taller then the main panel contents, then the panel
+            //    must grow to meet that new height. Otherwise, it must shrink.
+            //
+            // All three of these actions make use of CSS transformations, so they
+            // should all occur simultaneously.
+            this.setAttribute("viewtype", "subview");
+            this._shiftMainView(aAnchor);
+
+            this._mainViewHeight = this._viewStack.clientHeight;
+
+            let newHeight = this._heightOfSubview(viewNode, this._subViews);
+            this._setViewContainerHeight(newHeight);
+
+            this._subViewObserver.observe(viewNode, {
+              attributes: true,
+              characterData: true,
+              childList: true,
+              subtree: true
+            });
+          }.bind(this));
+        ]]></body>
+      </method>
+
+      <method name="_setViewContainerHeight">
+        <parameter name="aHeight"/>
+        <body><![CDATA[
+          let container = this._viewContainer;
+          this._transitioning = true;
+
+          let onTransitionEnd = () => {
+            container.removeEventListener("transitionend", onTransitionEnd);
+            this._transitioning = false;
+          };
+
+          container.addEventListener("transitionend", onTransitionEnd);
+          container.style.height = `${aHeight}px`;
+        ]]></body>
+      </method>
+
+      <method name="_shiftMainView">
+        <parameter name="aAnchor"/>
+        <body><![CDATA[
+          if (aAnchor) {
+            // We need to find the edge of the anchor, relative to the main panel.
+            // Then we need to add half the width of the anchor. This is the target
+            // that we need to transition to.
+            let anchorRect = aAnchor.getBoundingClientRect();
+            let mainViewRect = this._mainViewContainer.getBoundingClientRect();
+            let center = aAnchor.clientWidth / 2;
+            let direction = aAnchor.ownerDocument.defaultView.getComputedStyle(aAnchor, null).direction;
+            let edge;
+            if (direction == "ltr") {
+              edge = anchorRect.left - mainViewRect.left;
+            } else {
+              edge = mainViewRect.right - anchorRect.right;
+            }
+
+            // If the anchor is an element on the far end of the mainView we
+            // don't want to shift the mainView too far, we would reveal empty
+            // space otherwise.
+            let cstyle = window.getComputedStyle(document.documentElement, null);
+            let exitSubViewGutterWidth =
+              cstyle.getPropertyValue("--panel-ui-exit-subview-gutter-width");
+            let maxShift = mainViewRect.width - parseInt(exitSubViewGutterWidth);
+            let target = Math.min(maxShift, edge + center);
+
+            let neg = direction == "ltr" ? "-" : "";
+            this._mainViewContainer.style.transform = `translateX(${neg}${target}px)`;
+            aAnchor.setAttribute("panel-multiview-anchor", true);
+          } else {
+            this._mainViewContainer.style.transform = "";
+            if (this.anchorElement)
+              this.anchorElement.removeAttribute("panel-multiview-anchor");
+          }
+          this.anchorElement = aAnchor;
+        ]]></body>
+      </method>
+
+      <method name="handleEvent">
+        <parameter name="aEvent"/>
+        <body><![CDATA[
+          if (aEvent.type.startsWith("popup") && aEvent.target != this._panel) {
+            // Shouldn't act on e.g. context menus being shown from within the panel.
+            return;
+          }
+          switch (aEvent.type) {
+            case "click":
+              if (aEvent.originalTarget == this._clickCapturer) {
+                this.showMainView();
+              }
+              break;
+            case "overflow":
+              if (aEvent.target.localName == "vbox") {
+                // Resize the right view on the next tick.
+                if (this.showingSubView) {
+                  setTimeout(this._syncContainerWithSubView.bind(this), 0);
+                } else if (!this.transitioning) {
+                  setTimeout(this._syncContainerWithMainView.bind(this), 0);
+                }
+              }
+              break;
+            case "popupshowing":
+              this.setAttribute("panelopen", "true");
+              // Bug 941196 - The panel can get taller when opening a subview. Disabling
+              // autoPositioning means that the panel won't jump around if an opened
+              // subview causes the panel to exceed the dimensions of the screen in the
+              // direction that the panel originally opened in. This property resets
+              // every time the popup closes, which is why we have to set it each time.
+              this._panel.autoPosition = false;
+              this._syncContainerWithMainView();
+
+              this._mainViewObserver.observe(this._mainView, {
+                attributes: true,
+                characterData: true,
+                childList: true,
+                subtree: true
+              });
+
+              break;
+            case "popupshown":
+              this._setMaxHeight();
+              break;
+            case "popuphidden":
+              this.removeAttribute("panelopen");
+              this._mainView.style.removeProperty("height");
+              this.showMainView();
+              this._mainViewObserver.disconnect();
+              break;
+          }
+        ]]></body>
+      </method>
+
+      <method name="_shouldSetPosition">
+        <body><![CDATA[
+          return this.getAttribute("nosubviews") == "true";
+        ]]></body>
+      </method>
+
+      <method name="_shouldSetHeight">
+        <body><![CDATA[
+          return this.getAttribute("nosubviews") != "true";
+        ]]></body>
+      </method>
+
+      <method name="_setMaxHeight">
+        <body><![CDATA[
+          if (!this._shouldSetHeight())
+            return;
+
+          // Ignore the mutation that'll fire when we set the height of
+          // the main view.
+          this.ignoreMutations = true;
+          this._mainView.style.height =
+            this.getBoundingClientRect().height + "px";
+          this.ignoreMutations = false;
+        ]]></body>
+      </method>
+      <method name="_adjustContainerHeight">
+        <body><![CDATA[
+          if (!this.ignoreMutations && !this.showingSubView && !this._transitioning) {
+            let height;
+            if (this.showingSubViewAsMainView) {
+              height = this._heightOfSubview(this._mainView);
+            } else {
+              height = this._mainView.scrollHeight;
+            }
+            this._viewContainer.style.height = height + "px";
+          }
+        ]]></body>
+      </method>
+      <method name="_syncContainerWithSubView">
+        <body><![CDATA[
+          // Check that this panel is still alive:
+          if (!this._panel || !this._panel.parentNode) {
+            return;
+          }
+
+          if (!this.ignoreMutations && this.showingSubView) {
+            let newHeight = this._heightOfSubview(this._currentSubView, this._subViews);
+            this._viewContainer.style.height = newHeight + "px";
+          }
+        ]]></body>
+      </method>
+      <method name="_syncContainerWithMainView">
+        <body><![CDATA[
+          // Check that this panel is still alive:
+          if (!this._panel || !this._panel.parentNode) {
+            return;
+          }
+
+          if (this._shouldSetPosition()) {
+            this._panel.adjustArrowPosition();
+          }
+
+          if (this._shouldSetHeight()) {
+            this._adjustContainerHeight();
+          }
+        ]]></body>
+      </method>
+
+      <!-- Call this when the height of one of your views (the main view or a
+           subview) changes and you want the heights of the multiview and panel
+           to be the same as the view's height.
+           If the caller can give a hint of the expected height change with the
+           optional aExpectedChange parameter, it prevents flicker. -->
+      <method name="setHeightToFit">
+        <parameter name="aExpectedChange"/>
+        <body><![CDATA[
+          // Set the max-height to zero, wait until the height is actually
+          // updated, and then remove it.  If it's not removed, weird things can
+          // happen, like widgets in the panel won't respond to clicks even
+          // though they're visible.
+          let count = 5;
+          let height = getComputedStyle(this).height;
+          if (aExpectedChange)
+            this.style.maxHeight = (parseInt(height) + aExpectedChange) + "px";
+          else
+            this.style.maxHeight = "0";
+          let interval = setInterval(() => {
+            if (height != getComputedStyle(this).height || --count == 0) {
+              clearInterval(interval);
+              this.style.removeProperty("max-height");
+            }
+          }, 0);
+        ]]></body>
+      </method>
+
+      <method name="_heightOfSubview">
+        <parameter name="aSubview"/>
+        <parameter name="aContainerToCheck"/>
+        <body><![CDATA[
+          function getFullHeight(element) {
+            // XXXgijs: unfortunately, scrollHeight rounds values, and there's no alternative
+            // that works with overflow: auto elements. Fortunately for us,
+            // we have exactly 1 (potentially) scrolling element in here (the subview body),
+            // and rounding 1 value is OK - rounding more than 1 and adding them means we get
+            // off-by-1 errors. Now we might be off by a subpixel, but we care less about that.
+            // So, use scrollHeight *only* if the element is vertically scrollable.
+            let height;
+            let elementCS;
+            if (element.scrollTopMax) {
+              height = element.scrollHeight;
+              // Bounding client rects include borders, scrollHeight doesn't:
+              elementCS = win.getComputedStyle(element);
+              height += parseFloat(elementCS.borderTopWidth) +
+                        parseFloat(elementCS.borderBottomWidth);
+            } else {
+              height = element.getBoundingClientRect().height;
+              if (height > 0) {
+                elementCS = win.getComputedStyle(element);
+              }
+            }
+            if (elementCS) {
+              // Include margins - but not borders or paddings because they
+              // were dealt with above.
+              height += parseFloat(elementCS.marginTop) + parseFloat(elementCS.marginBottom);
+            }
+            return height;
+          }
+          let win = aSubview.ownerDocument.defaultView;
+          let body = aSubview.querySelector(".panel-subview-body");
+          let height = getFullHeight(body || aSubview);
+          if (body) {
+            let header = aSubview.querySelector(".panel-subview-header");
+            let footer = aSubview.querySelector(".panel-subview-footer");
+            height += (header ? getFullHeight(header) : 0) +
+                      (footer ? getFullHeight(footer) : 0);
+          }
+          if (aContainerToCheck) {
+            let containerCS = win.getComputedStyle(aContainerToCheck);
+            height += parseFloat(containerCS.paddingTop) + parseFloat(containerCS.paddingBottom);
+          }
+          return Math.ceil(height);
+        ]]></body>
+      </method>
+
+    </implementation>
+  </binding>
+
+  <binding id="panelview">
+    <implementation>
+      <property name="panelMultiView" readonly="true">
+        <getter><![CDATA[
+          if (this.parentNode.localName != "panelmultiview") {
+            return document.getBindingParent(this.parentNode);
+          }
+
+          return this.parentNode;
+        ]]></getter>
+      </property>
+    </implementation>
+  </binding>
+</bindings>
diff --git a/application/basilisk/components/customizableui/content/toolbar.xml b/application/basilisk/components/customizableui/content/toolbar.xml
new file mode 100644
index 000000000..a5cb10e6b
--- /dev/null
+++ b/application/basilisk/components/customizableui/content/toolbar.xml
@@ -0,0 +1,618 @@
+<?xml version="1.0"?>
+<!-- This Source Code Form is subject to the terms of the Mozilla Public
+   - License, v. 2.0. If a copy of the MPL was not distributed with this
+   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
+
+<bindings id="browserToolbarBindings"
+          xmlns="http://www.mozilla.org/xbl"
+          xmlns:xul="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+          xmlns:xbl="http://www.mozilla.org/xbl">
+
+  <binding id="toolbar" role="xul:toolbar">
+    <resources>
+      <stylesheet src="chrome://global/skin/toolbar.css"/>
+    </resources>
+    <implementation>
+      <field name="overflowedDuringConstruction">null</field>
+
+      <constructor><![CDATA[
+          let scope = {};
+          Cu.import("resource:///modules/CustomizableUI.jsm", scope);
+          // Add an early overflow event listener that will mark if the
+          // toolbar overflowed during construction.
+          if (scope.CustomizableUI.isAreaOverflowable(this.id)) {
+            this.addEventListener("overflow", this);
+            this.addEventListener("underflow", this);
+          }
+
+          if (document.readyState == "complete") {
+            this._init();
+          } else {
+            // Need to wait until XUL overlays are loaded. See bug 554279.
+            let self = this;
+            document.addEventListener("readystatechange", function onReadyStateChange() {
+              if (document.readyState != "complete")
+                return;
+              document.removeEventListener("readystatechange", onReadyStateChange);
+              self._init();
+            });
+          }
+      ]]></constructor>
+
+      <method name="_init">
+        <body><![CDATA[
+          let scope = {};
+          Cu.import("resource:///modules/CustomizableUI.jsm", scope);
+          let CustomizableUI = scope.CustomizableUI;
+
+          // Bug 989289: Forcibly set the now unsupported "mode" and "iconsize"
+          // attributes, just in case they accidentally get restored from
+          // persistence from a user that's been upgrading and downgrading.
+          if (CustomizableUI.isBuiltinToolbar(this.id)) {
+            const kAttributes = new Map([["mode", "icons"], ["iconsize", "small"]]);
+            for (let [attribute, value] of kAttributes) {
+              if (this.getAttribute(attribute) != value) {
+                this.setAttribute(attribute, value);
+                document.persist(this.id, attribute);
+              }
+              if (this.toolbox) {
+                if (this.toolbox.getAttribute(attribute) != value) {
+                  this.toolbox.setAttribute(attribute, value);
+                  document.persist(this.toolbox.id, attribute);
+                }
+              }
+            }
+          }
+
+          // Searching for the toolbox palette in the toolbar binding because
+          // toolbars are constructed first.
+          let toolbox = this.toolbox;
+          if (toolbox && !toolbox.palette) {
+            for (let node of toolbox.children) {
+              if (node.localName == "toolbarpalette") {
+                // Hold on to the palette but remove it from the document.
+                toolbox.palette = node;
+                toolbox.removeChild(node);
+                break;
+              }
+            }
+          }
+
+          // pass the current set of children for comparison with placements:
+          let children = Array.from(this.childNodes)
+                              .filter(node => node.getAttribute("skipintoolbarset") != "true" && node.id)
+                              .map(node => node.id);
+          CustomizableUI.registerToolbarNode(this, children);
+        ]]></body>
+      </method>
+
+      <method name="handleEvent">
+        <parameter name="aEvent"/>
+        <body><![CDATA[
+          if (aEvent.type == "overflow" && aEvent.detail > 0) {
+            if (this.overflowable && this.overflowable.initialized) {
+              this.overflowable.onOverflow(aEvent);
+            } else {
+              this.overflowedDuringConstruction = aEvent;
+            }
+          } else if (aEvent.type == "underflow" && aEvent.detail > 0) {
+            this.overflowedDuringConstruction = null;
+          }
+        ]]></body>
+      </method>
+
+      <method name="insertItem">
+        <parameter name="aId"/>
+        <parameter name="aBeforeElt"/>
+        <parameter name="aWrapper"/>
+        <body><![CDATA[
+          if (aWrapper) {
+            Cu.reportError("Can't insert " + aId + ": using insertItem " +
+                           "no longer supports wrapper elements.");
+            return null;
+          }
+
+          // Hack, the customizable UI code makes this be the last position
+          let pos = null;
+          if (aBeforeElt) {
+            let beforeInfo = CustomizableUI.getPlacementOfWidget(aBeforeElt.id);
+            if (beforeInfo.area != this.id) {
+              Cu.reportError("Can't insert " + aId + " before " +
+                             aBeforeElt.id + " which isn't in this area (" +
+                             this.id + ").");
+              return null;
+            }
+            pos = beforeInfo.position;
+          }
+
+          CustomizableUI.addWidgetToArea(aId, this.id, pos);
+          return this.ownerDocument.getElementById(aId);
+        ]]></body>
+      </method>
+
+      <property name="toolbarName"
+                onget="return this.getAttribute('toolbarname');"
+                onset="this.setAttribute('toolbarname', val); return val;"/>
+
+      <property name="customizationTarget" readonly="true">
+        <getter><![CDATA[
+          if (this._customizationTarget)
+            return this._customizationTarget;
+
+          let id = this.getAttribute("customizationtarget");
+          if (id)
+            this._customizationTarget = document.getElementById(id);
+
+          if (this._customizationTarget)
+            this._customizationTarget.insertItem = this.insertItem.bind(this);
+          else
+            this._customizationTarget = this;
+
+          return this._customizationTarget;
+        ]]></getter>
+      </property>
+
+      <property name="toolbox" readonly="true">
+        <getter><![CDATA[
+          if (this._toolbox)
+            return this._toolbox;
+
+          let toolboxId = this.getAttribute("toolboxid");
+          if (toolboxId) {
+            let toolbox = document.getElementById(toolboxId);
+            if (toolbox) {
+              if (toolbox.externalToolbars.indexOf(this) == -1)
+                toolbox.externalToolbars.push(this);
+
+              this._toolbox = toolbox;
+            }
+          }
+
+          if (!this._toolbox && this.parentNode &&
+              this.parentNode.localName == "toolbox") {
+            this._toolbox = this.parentNode;
+          }
+
+          return this._toolbox;
+        ]]></getter>
+      </property>
+
+      <property name="currentSet">
+        <getter><![CDATA[
+          let currentWidgets = new Set();
+          for (let node of this.customizationTarget.children) {
+            let realNode = node.localName == "toolbarpaletteitem" ? node.firstChild : node;
+            if (realNode.getAttribute("skipintoolbarset") != "true") {
+              currentWidgets.add(realNode.id);
+            }
+          }
+          if (this.getAttribute("overflowing") == "true") {
+            let overflowTarget = this.getAttribute("overflowtarget");
+            let overflowList = this.ownerDocument.getElementById(overflowTarget);
+            for (let node of overflowList.children) {
+              let realNode = node.localName == "toolbarpaletteitem" ? node.firstChild : node;
+              if (realNode.getAttribute("skipintoolbarset") != "true") {
+                currentWidgets.add(realNode.id);
+              }
+            }
+          }
+          let orderedPlacements = CustomizableUI.getWidgetIdsInArea(this.id);
+          return orderedPlacements.filter((x) => currentWidgets.has(x)).join(",");
+        ]]></getter>
+        <setter><![CDATA[
+          // Get list of new and old ids:
+          let newVal = (val || "").split(",").filter(x => x);
+          let oldIds = CustomizableUI.getWidgetIdsInArea(this.id);
+
+          // Get a list of items only in the new list
+          let newIds = newVal.filter(id => oldIds.indexOf(id) == -1);
+          CustomizableUI.beginBatchUpdate();
+          try {
+            for (let newId of newIds) {
+              oldIds = CustomizableUI.getWidgetIdsInArea(this.id);
+              let nextId = newId;
+              let pos;
+              do {
+                // Get the next item
+                nextId = newVal[newVal.indexOf(nextId) + 1];
+                // Figure out where it is in the old list
+                pos = oldIds.indexOf(nextId);
+                // If it's not in the old list, repeat:
+              } while (pos == -1 && nextId);
+              if (pos == -1) {
+                pos = null; // We didn't find anything, insert at the end
+              }
+              CustomizableUI.addWidgetToArea(newId, this.id, pos);
+            }
+
+            let currentIds = this.currentSet.split(",");
+            let removedIds = currentIds.filter(id => newIds.indexOf(id) == -1 && newVal.indexOf(id) == -1);
+            for (let removedId of removedIds) {
+              CustomizableUI.removeWidgetFromArea(removedId);
+            }
+          } finally {
+            CustomizableUI.endBatchUpdate();
+          }
+        ]]></setter>
+      </property>
+
+
+    </implementation>
+  </binding>
+
+  <binding id="toolbar-menubar-stub">
+    <implementation>
+      <property name="toolbox" readonly="true">
+        <getter><![CDATA[
+          if (this._toolbox)
+            return this._toolbox;
+
+          if (this.parentNode && this.parentNode.localName == "toolbox") {
+            this._toolbox = this.parentNode;
+          }
+
+          return this._toolbox;
+        ]]></getter>
+      </property>
+      <property name="currentSet" readonly="true">
+        <getter><![CDATA[
+          return this.getAttribute("defaultset");
+        ]]></getter>
+      </property>
+      <method name="insertItem">
+        <body><![CDATA[
+          return null;
+        ]]></body>
+      </method>
+    </implementation>
+  </binding>
+
+  <!-- The toolbar-menubar-autohide and toolbar-drag bindings are almost
+       verbatim copies of their toolkit counterparts - they just inherit from
+       the customizableui's toolbar binding instead of toolkit's. We're currently
+       OK with the maintainance burden of having two copies of a binding, since
+       the long term goal is to move the customization framework into toolkit. -->
+
+  <binding id="toolbar-menubar-autohide"
+           extends="chrome://browser/content/customizableui/toolbar.xml#toolbar">
+    <implementation>
+      <constructor>
+        this._setInactive();
+      </constructor>
+      <destructor>
+        this._setActive();
+      </destructor>
+
+      <field name="_inactiveTimeout">null</field>
+
+      <field name="_contextMenuListener"><![CDATA[({
+        toolbar: this,
+        contextMenu: null,
+
+        get active() {
+          return !!this.contextMenu;
+        },
+
+        init(event) {
+          let node = event.target;
+          while (node != this.toolbar) {
+            if (node.localName == "menupopup")
+              return;
+            node = node.parentNode;
+          }
+
+          let contextMenuId = this.toolbar.getAttribute("context");
+          if (!contextMenuId)
+            return;
+
+          this.contextMenu = document.getElementById(contextMenuId);
+          if (!this.contextMenu)
+            return;
+
+          this.contextMenu.addEventListener("popupshown", this);
+          this.contextMenu.addEventListener("popuphiding", this);
+          this.toolbar.addEventListener("mousemove", this);
+        },
+        handleEvent(event) {
+          switch (event.type) {
+            case "popupshown":
+              this.toolbar.removeEventListener("mousemove", this);
+              break;
+            case "popuphiding":
+            case "mousemove":
+              this.toolbar._setInactiveAsync();
+              this.toolbar.removeEventListener("mousemove", this);
+              this.contextMenu.removeEventListener("popuphiding", this);
+              this.contextMenu.removeEventListener("popupshown", this);
+              this.contextMenu = null;
+              break;
+          }
+        }
+      })]]></field>
+
+      <method name="_setInactive">
+        <body><![CDATA[
+          this.setAttribute("inactive", "true");
+        ]]></body>
+      </method>
+
+      <method name="_setInactiveAsync">
+        <body><![CDATA[
+          this._inactiveTimeout = setTimeout(function(self) {
+            if (self.getAttribute("autohide") == "true") {
+              self._inactiveTimeout = null;
+              self._setInactive();
+            }
+          }, 0, this);
+        ]]></body>
+      </method>
+
+      <method name="_setActive">
+        <body><![CDATA[
+          if (this._inactiveTimeout) {
+            clearTimeout(this._inactiveTimeout);
+            this._inactiveTimeout = null;
+          }
+          this.removeAttribute("inactive");
+        ]]></body>
+      </method>
+    </implementation>
+
+    <handlers>
+      <handler event="DOMMenuBarActive"     action="this._setActive();"/>
+      <handler event="popupshowing"         action="this._setActive();"/>
+      <handler event="mousedown" button="2" action="this._contextMenuListener.init(event);"/>
+      <handler event="DOMMenuBarInactive"><![CDATA[
+        if (!this._contextMenuListener.active)
+          this._setInactiveAsync();
+      ]]></handler>
+    </handlers>
+  </binding>
+
+  <binding id="toolbar-drag"
+           extends="chrome://browser/content/customizableui/toolbar.xml#toolbar">
+    <implementation>
+      <field name="_dragBindingAlive">true</field>
+      <constructor><![CDATA[
+        if (!this._draggableStarted) {
+          this._draggableStarted = true;
+          try {
+            let tmp = {};
+            Components.utils.import("resource://gre/modules/WindowDraggingUtils.jsm", tmp);
+            let draggableThis = new tmp.WindowDraggingElement(this);
+            draggableThis.mouseDownCheck = function(e) {
+              return this._dragBindingAlive;
+            };
+          } catch (e) {}
+        }
+      ]]></constructor>
+    </implementation>
+  </binding>
+
+
+<!-- This is a peculiar binding. It is here to deal with overlayed/inserted add-on content,
+      and immediately direct such content elsewhere. -->
+  <binding id="addonbar-delegating">
+    <implementation>
+      <constructor><![CDATA[
+          // Reading these immediately so nobody messes with them anymore:
+          this._delegatingToolbar = this.getAttribute("toolbar-delegate");
+          this._wasCollapsed = this.getAttribute("collapsed") == "true";
+          // Leaving those in here to unbreak some code:
+          if (document.readyState == "complete") {
+            this._init();
+          } else {
+            // Need to wait until XUL overlays are loaded. See bug 554279.
+            let self = this;
+            document.addEventListener("readystatechange", function onReadyStateChange() {
+              if (document.readyState != "complete")
+                return;
+              document.removeEventListener("readystatechange", onReadyStateChange);
+              self._init();
+            });
+          }
+      ]]></constructor>
+
+      <method name="_init">
+        <body><![CDATA[
+          // Searching for the toolbox palette in the toolbar binding because
+          // toolbars are constructed first.
+          let toolbox = this.toolbox;
+          if (toolbox && !toolbox.palette) {
+            for (let node of toolbox.children) {
+              if (node.localName == "toolbarpalette") {
+                // Hold on to the palette but remove it from the document.
+                toolbox.palette = node;
+                toolbox.removeChild(node);
+              }
+            }
+          }
+
+          // pass the current set of children for comparison with placements:
+          let children = [];
+          for (let node of this.childNodes) {
+            if (node.getAttribute("skipintoolbarset") != "true" && node.id) {
+              // Force everything to be removable so that buildArea can chuck stuff
+              // out if the user has customized things / we've been here before:
+              if (!this._whiteListed.has(node.id)) {
+                node.setAttribute("removable", "true");
+              }
+              children.push(node);
+            }
+          }
+          CustomizableUI.registerToolbarNode(this, children);
+          let existingMigratedItems = (this.getAttribute("migratedset") || "").split(",");
+          for (let migratedItem of existingMigratedItems.filter((x) => !!x)) {
+            this._currentSetMigrated.add(migratedItem);
+          }
+          this.evictNodes();
+          // We can't easily use |this| or strong bindings for the observer fn here
+          // because that creates leaky circular references when the node goes away,
+          // and XBL destructors are unreliable.
+          let mutationObserver = new MutationObserver(function(mutations) {
+            if (!mutations.length) {
+              return;
+            }
+            let toolbar = mutations[0].target;
+            // Can't use our own attribute because we might not have one if we're set to
+            // collapsed
+            let areCustomizing = toolbar.ownerDocument.documentElement.getAttribute("customizing");
+            if (!toolbar._isModifying && !areCustomizing) {
+              toolbar.evictNodes();
+            }
+          });
+          mutationObserver.observe(this, {childList: true});
+        ]]></body>
+      </method>
+      <method name="evictNodes">
+        <body><![CDATA[
+          this._isModifying = true;
+          let i = this.childNodes.length;
+          while (i--) {
+            let node = this.childNodes[i];
+            if (this.childNodes[i].id) {
+              this.evictNode(this.childNodes[i]);
+            } else {
+              node.remove();
+            }
+          }
+          this._isModifying = false;
+          this._updateMigratedSet();
+        ]]></body>
+      </method>
+      <method name="evictNode">
+        <parameter name="aNode"/>
+        <body>
+        <![CDATA[
+          if (this._whiteListed.has(aNode.id) || CustomizableUI.isSpecialWidget(aNode.id)) {
+            return;
+          }
+          const kItemMaxWidth = 100;
+          let oldParent = aNode.parentNode;
+          aNode.setAttribute("removable", "true");
+          this._currentSetMigrated.add(aNode.id);
+
+          let movedOut = false;
+          if (!this._wasCollapsed) {
+            try {
+              let nodeWidth = aNode.getBoundingClientRect().width;
+              if (nodeWidth == 0 || nodeWidth > kItemMaxWidth) {
+                throw new Error(aNode.id + " is too big (" + nodeWidth +
+                                "px wide), moving to the palette");
+              }
+              CustomizableUI.addWidgetToArea(aNode.id, this._delegatingToolbar);
+              movedOut = true;
+            } catch (ex) {
+              // This will throw if the node is too big, or can't be moved there for
+              // some reason. Report this:
+              Cu.reportError(ex);
+            }
+          }
+
+          /* We won't have moved the widget if either the add-on bar was collapsed,
+           * or if it was too wide to be inserted into the navbar. */
+          if (!movedOut) {
+            try {
+              CustomizableUI.removeWidgetFromArea(aNode.id);
+            } catch (ex) {
+              Cu.reportError(ex);
+              aNode.remove();
+            }
+          }
+
+          // Surprise: addWidgetToArea(palette) will get you nothing if the palette
+          // is not constructed yet. Fix:
+          if (aNode.parentNode == oldParent) {
+            let palette = this.toolbox.palette;
+            if (palette && oldParent != palette) {
+              palette.appendChild(aNode);
+            }
+          }
+        ]]></body>
+      </method>
+      <method name="insertItem">
+        <parameter name="aId"/>
+        <parameter name="aBeforeElt"/>
+        <parameter name="aWrapper"/>
+        <body><![CDATA[
+          if (aWrapper) {
+            Cu.reportError("Can't insert " + aId + ": using insertItem " +
+                           "no longer supports wrapper elements.");
+            return null;
+          }
+
+          let widget = CustomizableUI.getWidget(aId);
+          widget = widget && widget.forWindow(window);
+          let node = widget && widget.node;
+          if (!node) {
+            return null;
+          }
+
+          this._isModifying = true;
+          // Temporarily add it here so it can have a width, then ditch it:
+          this.appendChild(node);
+          this.evictNode(node);
+          this._isModifying = false;
+          this._updateMigratedSet();
+          // We will now have moved stuff around; kick off some events
+          // so add-ons know we've just moved their stuff:
+          // XXXgijs: only in this window. It's hard to know for sure what's the right
+          // thing to do here - typically insertItem is used on each window, so
+          // this seems to make the most sense, even if some of the effects of
+          // evictNode might affect multiple windows.
+          CustomizableUI.dispatchToolboxEvent("customizationchange", {}, window);
+          CustomizableUI.dispatchToolboxEvent("aftercustomization", {}, window);
+          return node;
+        ]]></body>
+      </method>
+      <method name="getMigratedItems">
+        <body><![CDATA[
+          return [...this._currentSetMigrated];
+        ]]></body>
+      </method>
+      <method name="_updateMigratedSet">
+        <body><![CDATA[
+          let newMigratedItems = this.getMigratedItems().join(",");
+          if (this.getAttribute("migratedset") != newMigratedItems) {
+            this.setAttribute("migratedset", newMigratedItems);
+            this.ownerDocument.persist(this.id, "migratedset");
+          }
+        ]]></body>
+      </method>
+      <property name="customizationTarget" readonly="true">
+        <getter><![CDATA[
+          return this;
+        ]]></getter>
+      </property>
+      <property name="currentSet">
+        <getter><![CDATA[
+          return Array.from(this.children, node => node.id).join(",");
+        ]]></getter>
+        <setter><![CDATA[
+          let v = val.split(",");
+          let newButtons = v.filter(x => x && (!this._whiteListed.has(x) &&
+                                               !CustomizableUI.isSpecialWidget(x) &&
+                                               !this._currentSetMigrated.has(x)));
+          for (let newButton of newButtons) {
+            this._currentSetMigrated.add(newButton);
+            this.insertItem(newButton);
+          }
+          this._updateMigratedSet();
+        ]]></setter>
+      </property>
+      <property name="toolbox" readonly="true">
+        <getter><![CDATA[
+          if (!this._toolbox && this.parentNode &&
+              this.parentNode.localName == "toolbox") {
+            this._toolbox = this.parentNode;
+          }
+
+          return this._toolbox;
+        ]]></getter>
+      </property>
+      <field name="_whiteListed" readonly="true">new Set(["addonbar-closebutton", "status-bar"])</field>
+      <field name="_isModifying">false</field>
+      <field name="_currentSetMigrated">new Set()</field>
+    </implementation>
+  </binding>
+</bindings>
diff --git a/application/basilisk/components/customizableui/moz.build b/application/basilisk/components/customizableui/moz.build
new file mode 100644
index 000000000..f22a449da
--- /dev/null
+++ b/application/basilisk/components/customizableui/moz.build
@@ -0,0 +1,27 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DIRS += [
+    'content',
+]
+
+EXTRA_JS_MODULES += [
+    'DragPositionManager.jsm',
+    'PanelWideWidgetTracker.jsm',
+    'ScrollbarSampler.jsm',
+]
+
+EXTRA_PP_JS_MODULES += [
+    'CustomizableUI.jsm',
+    'CustomizableWidgets.jsm',
+    'CustomizeMode.jsm',
+]
+
+if CONFIG['MOZ_WIDGET_TOOLKIT'] in ('windows', 'cocoa'):
+    DEFINES['CAN_DRAW_IN_TITLEBAR'] = 1
+
+if CONFIG['MOZ_WIDGET_TOOLKIT'] in ('windows', 'gtk2', 'gtk3'):
+    DEFINES['MENUBAR_CAN_AUTOHIDE'] = 1
\ No newline at end of file