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diff --git a/base/content/browser-gestureSupport.js b/base/content/browser-gestureSupport.js
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+# 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/.
+
+// Simple gestures support
+//
+// As per bug #412486, web content must not be allowed to receive any
+// simple gesture events.  Multi-touch gesture APIs are in their
+// infancy and we do NOT want to be forced into supporting an API that
+// will probably have to change in the future.  (The current Mac OS X
+// API is undocumented and was reverse-engineered.)  Until support is
+// implemented in the event dispatcher to keep these events as
+// chrome-only, we must listen for the simple gesture events during
+// the capturing phase and call stopPropagation on every event.
+
+var gGestureSupport = {
+  _currentRotation: 0,
+  _lastRotateDelta: 0,
+  _rotateMomentumThreshold: .75,
+
+  /**
+   * Add or remove mouse gesture event listeners
+   *
+   * @param aAddListener
+   *        True to add/init listeners and false to remove/uninit
+   */
+  init: function GS_init(aAddListener) {
+    // Bug 863514 - Make gesture support work in electrolysis
+    if (gMultiProcessBrowser)
+      return;
+
+    const gestureEvents = ["SwipeGestureStart",
+      "SwipeGestureUpdate", "SwipeGestureEnd", "SwipeGesture",
+      "MagnifyGestureStart", "MagnifyGestureUpdate", "MagnifyGesture",
+      "RotateGestureStart", "RotateGestureUpdate", "RotateGesture",
+      "TapGesture", "PressTapGesture"];
+
+    let addRemove = aAddListener ? window.addEventListener :
+      window.removeEventListener;
+
+    gestureEvents.forEach(function (event) addRemove("Moz" + event, this, true),
+                          this);
+  },
+
+  /**
+   * Dispatch events based on the type of mouse gesture event. For now, make
+   * sure to stop propagation of every gesture event so that web content cannot
+   * receive gesture events.
+   *
+   * @param aEvent
+   *        The gesture event to handle
+   */
+  handleEvent: function GS_handleEvent(aEvent) {
+    if (!Services.prefs.getBoolPref(
+           "dom.debug.propagate_gesture_events_through_content")) {
+      aEvent.stopPropagation();
+    }
+
+    // Create a preference object with some defaults
+    let def = function(aThreshold, aLatched)
+      ({ threshold: aThreshold, latched: !!aLatched });
+
+    switch (aEvent.type) {
+      case "MozSwipeGestureStart":
+        aEvent.preventDefault();
+        this._setupSwipeGesture(aEvent);
+        break;
+      case "MozSwipeGestureUpdate":
+        aEvent.preventDefault();
+        this._doUpdate(aEvent);
+        break;
+      case "MozSwipeGestureEnd":
+        aEvent.preventDefault();
+        this._doEnd(aEvent);
+        break;
+      case "MozSwipeGesture":
+        aEvent.preventDefault();
+        this.onSwipe(aEvent);
+        break;
+      case "MozMagnifyGestureStart":
+        aEvent.preventDefault();
+#ifdef XP_WIN
+        this._setupGesture(aEvent, "pinch", def(25, 0), "out", "in");
+#else
+        this._setupGesture(aEvent, "pinch", def(150, 1), "out", "in");
+#endif
+        break;
+      case "MozRotateGestureStart":
+        aEvent.preventDefault();
+        this._setupGesture(aEvent, "twist", def(25, 0), "right", "left");
+        break;
+      case "MozMagnifyGestureUpdate":
+      case "MozRotateGestureUpdate":
+        aEvent.preventDefault();
+        this._doUpdate(aEvent);
+        break;
+      case "MozTapGesture":
+        aEvent.preventDefault();
+        this._doAction(aEvent, ["tap"]);
+        break;
+      case "MozRotateGesture":
+        aEvent.preventDefault();
+        this._doAction(aEvent, ["twist", "end"]);
+        break;
+      /* case "MozPressTapGesture":
+        break; */
+    }
+  },
+
+  /**
+   * Called at the start of "pinch" and "twist" gestures to setup all of the
+   * information needed to process the gesture
+   *
+   * @param aEvent
+   *        The continual motion start event to handle
+   * @param aGesture
+   *        Name of the gesture to handle
+   * @param aPref
+   *        Preference object with the names of preferences and defaults
+   * @param aInc
+   *        Command to trigger for increasing motion (without gesture name)
+   * @param aDec
+   *        Command to trigger for decreasing motion (without gesture name)
+   */
+  _setupGesture: function GS__setupGesture(aEvent, aGesture, aPref, aInc, aDec) {
+    // Try to load user-set values from preferences
+    for (let [pref, def] in Iterator(aPref))
+      aPref[pref] = this._getPref(aGesture + "." + pref, def);
+
+    // Keep track of the total deltas and latching behavior
+    let offset = 0;
+    let latchDir = aEvent.delta > 0 ? 1 : -1;
+    let isLatched = false;
+
+    // Create the update function here to capture closure state
+    this._doUpdate = function GS__doUpdate(aEvent) {
+      // Update the offset with new event data
+      offset += aEvent.delta;
+
+      // Check if the cumulative deltas exceed the threshold
+      if (Math.abs(offset) > aPref["threshold"]) {
+        // Trigger the action if we don't care about latching; otherwise, make
+        // sure either we're not latched and going the same direction of the
+        // initial motion; or we're latched and going the opposite way
+        let sameDir = (latchDir ^ offset) >= 0;
+        if (!aPref["latched"] || (isLatched ^ sameDir)) {
+          this._doAction(aEvent, [aGesture, offset > 0 ? aInc : aDec]);
+
+          // We must be getting latched or leaving it, so just toggle
+          isLatched = !isLatched;
+        }
+
+        // Reset motion counter to prepare for more of the same gesture
+        offset = 0;
+      }
+    };
+
+    // The start event also contains deltas, so handle an update right away
+    this._doUpdate(aEvent);
+  },
+
+  /**
+   * Checks whether a swipe gesture event can navigate the browser history or
+   * not.
+   *
+   * @param aEvent
+   *        The swipe gesture event.
+   * @return true if the swipe event may navigate the history, false othwerwise.
+   */
+  _swipeNavigatesHistory: function GS__swipeNavigatesHistory(aEvent) {
+    return this._getCommand(aEvent, ["swipe", "left"])
+              == "Browser:BackOrBackDuplicate" &&
+           this._getCommand(aEvent, ["swipe", "right"])
+              == "Browser:ForwardOrForwardDuplicate";
+  },
+
+  /**
+   * Sets up the history swipe animations for a swipe gesture event, if enabled.
+   *
+   * @param aEvent
+   *        The swipe gesture start event.
+   */
+  _setupSwipeGesture: function GS__setupSwipeGesture(aEvent) {
+    if (!this._swipeNavigatesHistory(aEvent))
+      return;
+
+    let canGoBack = gHistorySwipeAnimation.canGoBack();
+    let canGoForward = gHistorySwipeAnimation.canGoForward();
+    let isLTR = gHistorySwipeAnimation.isLTR;
+
+    if (canGoBack)
+      aEvent.allowedDirections |= isLTR ? aEvent.DIRECTION_LEFT :
+                                          aEvent.DIRECTION_RIGHT;
+    if (canGoForward)
+      aEvent.allowedDirections |= isLTR ? aEvent.DIRECTION_RIGHT :
+                                          aEvent.DIRECTION_LEFT;
+
+    gHistorySwipeAnimation.startAnimation();
+
+    this._doUpdate = function GS__doUpdate(aEvent) {
+      gHistorySwipeAnimation.updateAnimation(aEvent.delta);
+    };
+
+    this._doEnd = function GS__doEnd(aEvent) {
+      gHistorySwipeAnimation.swipeEndEventReceived();
+
+      this._doUpdate = function (aEvent) {};
+      this._doEnd = function (aEvent) {};
+    }
+  },
+
+  /**
+   * Generator producing the powerset of the input array where the first result
+   * is the complete set and the last result (before StopIteration) is empty.
+   *
+   * @param aArray
+   *        Source array containing any number of elements
+   * @yield Array that is a subset of the input array from full set to empty
+   */
+  _power: function GS__power(aArray) {
+    // Create a bitmask based on the length of the array
+    let num = 1 << aArray.length;
+    while (--num >= 0) {
+      // Only select array elements where the current bit is set
+      yield aArray.reduce(function (aPrev, aCurr, aIndex) {
+        if (num & 1 << aIndex)
+          aPrev.push(aCurr);
+        return aPrev;
+      }, []);
+    }
+  },
+
+  /**
+   * Determine what action to do for the gesture based on which keys are
+   * pressed and which commands are set, and execute the command.
+   *
+   * @param aEvent
+   *        The original gesture event to convert into a fake click event
+   * @param aGesture
+   *        Array of gesture name parts (to be joined by periods)
+   * @return Name of the executed command. Returns null if no command is
+   *         found.
+   */
+  _doAction: function GS__doAction(aEvent, aGesture) {
+    let command = this._getCommand(aEvent, aGesture);
+    return command && this._doCommand(aEvent, command);
+  },
+
+  /**
+   * Determine what action to do for the gesture based on which keys are
+   * pressed and which commands are set
+   *
+   * @param aEvent
+   *        The original gesture event to convert into a fake click event
+   * @param aGesture
+   *        Array of gesture name parts (to be joined by periods)
+   */
+  _getCommand: function GS__getCommand(aEvent, aGesture) {
+    // Create an array of pressed keys in a fixed order so that a command for
+    // "meta" is preferred over "ctrl" when both buttons are pressed (and a
+    // command for both don't exist)
+    let keyCombos = [];
+    ["shift", "alt", "ctrl", "meta"].forEach(function (key) {
+      if (aEvent[key + "Key"])
+        keyCombos.push(key);
+    });
+
+    // Try each combination of key presses in decreasing order for commands
+    for (let subCombo of this._power(keyCombos)) {
+      // Convert a gesture and pressed keys into the corresponding command
+      // action where the preference has the gesture before "shift" before
+      // "alt" before "ctrl" before "meta" all separated by periods
+      let command;
+      try {
+        command = this._getPref(aGesture.concat(subCombo).join("."));
+      } catch (e) {}
+
+      if (command)
+        return command;
+    }
+    return null;
+  },
+
+  /**
+   * Execute the specified command.
+   *
+   * @param aEvent
+   *        The original gesture event to convert into a fake click event
+   * @param aCommand
+   *        Name of the command found for the event's keys and gesture.
+   */
+  _doCommand: function GS__doCommand(aEvent, aCommand) {
+    let node = document.getElementById(aCommand);
+    if (node) {
+      if (node.getAttribute("disabled") != "true") {
+        let cmdEvent = document.createEvent("xulcommandevent");
+        cmdEvent.initCommandEvent("command", true, true, window, 0,
+                                  aEvent.ctrlKey, aEvent.altKey,
+                                  aEvent.shiftKey, aEvent.metaKey, aEvent);
+        node.dispatchEvent(cmdEvent);
+      }
+
+    }
+    else {
+      goDoCommand(aCommand);
+    }
+  },
+
+  /**
+   * Handle continual motion events.  This function will be set by
+   * _setupGesture or _setupSwipe.
+   *
+   * @param aEvent
+   *        The continual motion update event to handle
+   */
+  _doUpdate: function(aEvent) {},
+
+  /**
+   * Handle gesture end events.  This function will be set by _setupSwipe.
+   *
+   * @param aEvent
+   *        The gesture end event to handle
+   */
+  _doEnd: function(aEvent) {},
+
+  /**
+   * Convert the swipe gesture into a browser action based on the direction.
+   *
+   * @param aEvent
+   *        The swipe event to handle
+   */
+  onSwipe: function GS_onSwipe(aEvent) {
+    // Figure out which one (and only one) direction was triggered
+    for (let dir of ["UP", "RIGHT", "DOWN", "LEFT"]) {
+      if (aEvent.direction == aEvent["DIRECTION_" + dir]) {
+        this._coordinateSwipeEventWithAnimation(aEvent, dir);
+        break;
+      }
+    }
+  },
+
+  /**
+   * Process a swipe event based on the given direction.
+   *
+   * @param aEvent
+   *        The swipe event to handle
+   * @param aDir
+   *        The direction for the swipe event
+   */
+  processSwipeEvent: function GS_processSwipeEvent(aEvent, aDir) {
+    this._doAction(aEvent, ["swipe", aDir.toLowerCase()]);
+  },
+
+  /**
+   * Coordinates the swipe event with the swipe animation, if any.
+   * If an animation is currently running, the swipe event will be
+   * processed once the animation stops. This will guarantee a fluid
+   * motion of the animation.
+   *
+   * @param aEvent
+   *        The swipe event to handle
+   * @param aDir
+   *        The direction for the swipe event
+   */
+  _coordinateSwipeEventWithAnimation:
+  function GS__coordinateSwipeEventWithAnimation(aEvent, aDir) {
+    if ((gHistorySwipeAnimation.isAnimationRunning()) &&
+        (aDir == "RIGHT" || aDir == "LEFT")) {
+      gHistorySwipeAnimation.processSwipeEvent(aEvent, aDir);
+    }
+    else {
+      this.processSwipeEvent(aEvent, aDir);
+    }
+  },
+
+  /**
+   * Get a gesture preference or use a default if it doesn't exist
+   *
+   * @param aPref
+   *        Name of the preference to load under the gesture branch
+   * @param aDef
+   *        Default value if the preference doesn't exist
+   */
+  _getPref: function GS__getPref(aPref, aDef) {
+    // Preferences branch under which all gestures preferences are stored
+    const branch = "browser.gesture.";
+
+    try {
+      // Determine what type of data to load based on default value's type
+      let type = typeof aDef;
+      let getFunc = "get" + (type == "boolean" ? "Bool" :
+                             type == "number" ? "Int" : "Char") + "Pref";
+      return gPrefService[getFunc](branch + aPref);
+    }
+    catch (e) {
+      return aDef;
+    }
+  },
+
+  /**
+   * Perform rotation for ImageDocuments
+   *
+   * @param aEvent
+   *        The MozRotateGestureUpdate event triggering this call
+   */
+  rotate: function(aEvent) {
+    if (!(content.document instanceof ImageDocument))
+      return;
+
+    let contentElement = content.document.body.firstElementChild;
+    if (!contentElement)
+      return;
+    // If we're currently snapping, cancel that snap
+    if (contentElement.classList.contains("completeRotation"))
+      this._clearCompleteRotation();
+
+    this.rotation = Math.round(this.rotation + aEvent.delta);
+    contentElement.style.transform = "rotate(" + this.rotation + "deg)";
+    this._lastRotateDelta = aEvent.delta;
+  },
+
+  /**
+   * Perform a rotation end for ImageDocuments
+   */
+  rotateEnd: function() {
+    if (!(content.document instanceof ImageDocument))
+      return;
+
+    let contentElement = content.document.body.firstElementChild;
+    if (!contentElement)
+      return;
+
+    let transitionRotation = 0;
+
+    // The reason that 360 is allowed here is because when rotating between
+    // 315 and 360, setting rotate(0deg) will cause it to rotate the wrong
+    // direction around--spinning wildly.
+    if (this.rotation <= 45)
+      transitionRotation = 0;
+    else if (this.rotation > 45 && this.rotation <= 135)
+      transitionRotation = 90;
+    else if (this.rotation > 135 && this.rotation <= 225)
+      transitionRotation = 180;
+    else if (this.rotation > 225 && this.rotation <= 315)
+      transitionRotation = 270;
+    else
+      transitionRotation = 360;
+
+    // If we're going fast enough, and we didn't already snap ahead of rotation,
+    // then snap ahead of rotation to simulate momentum
+    if (this._lastRotateDelta > this._rotateMomentumThreshold &&
+        this.rotation > transitionRotation)
+      transitionRotation += 90;
+    else if (this._lastRotateDelta < -1 * this._rotateMomentumThreshold &&
+             this.rotation < transitionRotation)
+      transitionRotation -= 90;
+
+    // Only add the completeRotation class if it is is necessary
+    if (transitionRotation != this.rotation) {
+      contentElement.classList.add("completeRotation");
+      contentElement.addEventListener("transitionend", this._clearCompleteRotation);
+    }
+
+    contentElement.style.transform = "rotate(" + transitionRotation + "deg)";
+    this.rotation = transitionRotation;
+  },
+
+  /**
+   * Gets the current rotation for the ImageDocument
+   */
+  get rotation() {
+    return this._currentRotation;
+  },
+
+  /**
+   * Sets the current rotation for the ImageDocument
+   *
+   * @param aVal
+   *        The new value to take.  Can be any value, but it will be bounded to
+   *        0 inclusive to 360 exclusive.
+   */
+  set rotation(aVal) {
+    this._currentRotation = aVal % 360;
+    if (this._currentRotation < 0)
+      this._currentRotation += 360;
+    return this._currentRotation;
+  },
+
+  /**
+   * When the location/tab changes, need to reload the current rotation for the
+   * image
+   */
+  restoreRotationState: function() {
+    // Bug 863514 - Make gesture support work in electrolysis
+    if (gMultiProcessBrowser)
+      return;
+
+    if (!(content.document instanceof ImageDocument))
+      return;
+
+    let contentElement = content.document.body.firstElementChild;
+    let transformValue = content.window.getComputedStyle(contentElement, null)
+                                       .transform;
+
+    if (transformValue == "none") {
+      this.rotation = 0;
+      return;
+    }
+
+    // transformValue is a rotation matrix--split it and do mathemagic to
+    // obtain the real rotation value
+    transformValue = transformValue.split("(")[1]
+                                   .split(")")[0]
+                                   .split(",");
+    this.rotation = Math.round(Math.atan2(transformValue[1], transformValue[0]) *
+                               (180 / Math.PI));
+  },
+
+  /**
+   * Removes the transition rule by removing the completeRotation class
+   */
+  _clearCompleteRotation: function() {
+    let contentElement = content.document &&
+                         content.document instanceof ImageDocument &&
+                         content.document.body &&
+                         content.document.body.firstElementChild;
+    if (!contentElement)
+      return;
+    contentElement.classList.remove("completeRotation");
+    contentElement.removeEventListener("transitionend", this._clearCompleteRotation);
+  },
+};
+
+// History Swipe Animation Support (bug 678392)
+var gHistorySwipeAnimation = {
+
+  active: false,
+  isLTR: false,
+
+  /**
+   * Initializes the support for history swipe animations, if it is supported
+   * by the platform/configuration.
+   */
+  init: function HSA_init() {
+    if (!this._isSupported())
+      return;
+
+    this.active = false;
+    this.isLTR = document.documentElement.mozMatchesSelector(
+                                            ":-moz-locale-dir(ltr)");
+    this._trackedSnapshots = [];
+    this._historyIndex = -1;
+    this._boxWidth = -1;
+    this._maxSnapshots = this._getMaxSnapshots();
+    this._lastSwipeDir = "";
+
+    // We only want to activate history swipe animations if we store snapshots.
+    // If we don't store any, we handle horizontal swipes without animations.
+    if (this._maxSnapshots > 0) {
+      this.active = true;
+      gBrowser.addEventListener("pagehide", this, false);
+      gBrowser.addEventListener("pageshow", this, false);
+      gBrowser.addEventListener("popstate", this, false);
+      gBrowser.tabContainer.addEventListener("TabClose", this, false);
+    }
+  },
+
+  /**
+   * Uninitializes the support for history swipe animations.
+   */
+  uninit: function HSA_uninit() {
+    gBrowser.removeEventListener("pagehide", this, false);
+    gBrowser.removeEventListener("pageshow", this, false);
+    gBrowser.removeEventListener("popstate", this, false);
+    gBrowser.tabContainer.removeEventListener("TabClose", this, false);
+
+    this.active = false;
+    this.isLTR = false;
+  },
+
+  /**
+   * Starts the swipe animation and handles fast swiping (i.e. a swipe animation
+   * is already in progress when a new one is initiated).
+   */
+  startAnimation: function HSA_startAnimation() {
+    if (this.isAnimationRunning()) {
+      gBrowser.stop();
+      this._lastSwipeDir = "RELOAD"; // just ensure that != ""
+      this._canGoBack = this.canGoBack();
+      this._canGoForward = this.canGoForward();
+      this._handleFastSwiping();
+    }
+    else {
+      this._historyIndex = gBrowser.webNavigation.sessionHistory.index;
+      this._canGoBack = this.canGoBack();
+      this._canGoForward = this.canGoForward();
+      if (this.active) {
+        this._takeSnapshot();
+        this._installPrevAndNextSnapshots();
+        this._addBoxes();
+        this._lastSwipeDir = "";
+      }
+    }
+    this.updateAnimation(0);
+  },
+
+  /**
+   * Stops the swipe animation.
+   */
+  stopAnimation: function HSA_stopAnimation() {
+    gHistorySwipeAnimation._removeBoxes();
+  },
+
+  /**
+   * Updates the animation between two pages in history.
+   *
+   * @param aVal
+   *        A floating point value that represents the progress of the
+   *        swipe gesture.
+   */
+  updateAnimation: function HSA_updateAnimation(aVal) {
+    if (!this.isAnimationRunning())
+      return;
+
+    if ((aVal >= 0 && this.isLTR) ||
+        (aVal <= 0 && !this.isLTR)) {
+      if (aVal > 1)
+        aVal = 1; // Cap value to avoid sliding the page further than allowed.
+
+      if (this._canGoBack)
+        this._prevBox.collapsed = false;
+      else
+        this._prevBox.collapsed = true;
+
+      // The current page is pushed to the right (LTR) or left (RTL),
+      // the intention is to go back.
+      // If there is a page to go back to, it should show in the background.
+      this._positionBox(this._curBox, aVal);
+
+      // The forward page should be pushed offscreen all the way to the right.
+      this._positionBox(this._nextBox, 1);
+    }
+    else {
+      if (aVal < -1)
+        aVal = -1; // Cap value to avoid sliding the page further than allowed.
+
+      // The intention is to go forward. If there is a page to go forward to,
+      // it should slide in from the right (LTR) or left (RTL).
+      // Otherwise, the current page should slide to the left (LTR) or
+      // right (RTL) and the backdrop should appear in the background.
+      // For the backdrop to be visible in that case, the previous page needs
+      // to be hidden (if it exists).
+      if (this._canGoForward) {
+        let offset = this.isLTR ? 1 : -1;
+        this._positionBox(this._curBox, 0);
+        this._positionBox(this._nextBox, offset + aVal); // aVal is negative
+      }
+      else {
+        this._prevBox.collapsed = true;
+        this._positionBox(this._curBox, aVal);
+      }
+    }
+  },
+
+  /**
+   * Event handler for events relevant to the history swipe animation.
+   *
+   * @param aEvent
+   *        An event to process.
+   */
+  handleEvent: function HSA_handleEvent(aEvent) {
+    switch (aEvent.type) {
+      case "TabClose":
+        let browser = gBrowser.getBrowserForTab(aEvent.target);
+        this._removeTrackedSnapshot(-1, browser);
+        break;
+      case "pageshow":
+      case "popstate":
+        if (this.isAnimationRunning()) {
+          if (aEvent.target != gBrowser.selectedBrowser.contentDocument)
+            break;
+          this.stopAnimation();
+        }
+        this._historyIndex = gBrowser.webNavigation.sessionHistory.index;
+        break;
+      case "pagehide":
+        if (aEvent.target == gBrowser.selectedBrowser.contentDocument) {
+          // Take a snapshot of a page whenever it's about to be navigated away
+          // from.
+          this._takeSnapshot();
+        }
+        break;
+    }
+  },
+
+  /**
+   * Checks whether the history swipe animation is currently running or not.
+   *
+   * @return true if the animation is currently running, false otherwise.
+   */
+  isAnimationRunning: function HSA_isAnimationRunning() {
+    return !!this._container;
+  },
+
+  /**
+   * Process a swipe event based on the given direction.
+   *
+   * @param aEvent
+   *        The swipe event to handle
+   * @param aDir
+   *        The direction for the swipe event
+   */
+  processSwipeEvent: function HSA_processSwipeEvent(aEvent, aDir) {
+    if (aDir == "RIGHT")
+      this._historyIndex += this.isLTR ? 1 : -1;
+    else if (aDir == "LEFT")
+      this._historyIndex += this.isLTR ? -1 : 1;
+    else
+      return;
+    this._lastSwipeDir = aDir;
+  },
+
+  /**
+   * Checks if there is a page in the browser history to go back to.
+   *
+   * @return true if there is a previous page in history, false otherwise.
+   */
+  canGoBack: function HSA_canGoBack() {
+    if (this.isAnimationRunning())
+      return this._doesIndexExistInHistory(this._historyIndex - 1);
+    return gBrowser.webNavigation.canGoBack;
+  },
+
+  /**
+   * Checks if there is a page in the browser history to go forward to.
+   *
+   * @return true if there is a next page in history, false otherwise.
+   */
+  canGoForward: function HSA_canGoForward() {
+    if (this.isAnimationRunning())
+      return this._doesIndexExistInHistory(this._historyIndex + 1);
+    return gBrowser.webNavigation.canGoForward;
+  },
+
+  /**
+   * Used to notify the history swipe animation that the OS sent a swipe end
+   * event and that we should navigate to the page that the user swiped to, if
+   * any. This will also result in the animation overlay to be torn down.
+   */
+  swipeEndEventReceived: function HSA_swipeEndEventReceived() {
+    if (this._lastSwipeDir != "")
+      this._navigateToHistoryIndex();
+    else
+      this.stopAnimation();
+  },
+
+  /**
+   * Checks whether a particular index exists in the browser history or not.
+   *
+   * @param aIndex
+   *        The index to check for availability for in the history.
+   * @return true if the index exists in the browser history, false otherwise.
+   */
+  _doesIndexExistInHistory: function HSA__doesIndexExistInHistory(aIndex) {
+    try {
+      gBrowser.webNavigation.sessionHistory.getEntryAtIndex(aIndex, false);
+    }
+    catch(ex) {
+      return false;
+    }
+    return true;
+  },
+
+  /**
+   * Navigates to the index in history that is currently being tracked by
+   * |this|.
+   */
+  _navigateToHistoryIndex: function HSA__navigateToHistoryIndex() {
+    if (this._doesIndexExistInHistory(this._historyIndex)) {
+      gBrowser.webNavigation.gotoIndex(this._historyIndex);
+    }
+  },
+
+  /**
+   * Checks to see if history swipe animations are supported by this
+   * platform/configuration.
+   *
+   * return true if supported, false otherwise.
+   */
+  _isSupported: function HSA__isSupported() {
+    return window.matchMedia("(-moz-swipe-animation-enabled)").matches;
+  },
+
+  /**
+   * Handle fast swiping (i.e. a swipe animation is already in
+   * progress when a new one is initiated). This will swap out the snapshots
+   * used in the previous animation with the appropriate new ones.
+   */
+  _handleFastSwiping: function HSA__handleFastSwiping() {
+    this._installCurrentPageSnapshot(null);
+    this._installPrevAndNextSnapshots();
+  },
+
+  /**
+   * Adds the boxes that contain the snapshots used during the swipe animation.
+   */
+  _addBoxes: function HSA__addBoxes() {
+    let browserStack =
+      document.getAnonymousElementByAttribute(gBrowser.getNotificationBox(),
+                                              "class", "browserStack");
+    this._container = this._createElement("historySwipeAnimationContainer",
+                                          "stack");
+    browserStack.appendChild(this._container);
+
+    this._prevBox = this._createElement("historySwipeAnimationPreviousPage",
+                                        "box");
+    this._container.appendChild(this._prevBox);
+
+    this._curBox = this._createElement("historySwipeAnimationCurrentPage",
+                                       "box");
+    this._container.appendChild(this._curBox);
+
+    this._nextBox = this._createElement("historySwipeAnimationNextPage",
+                                        "box");
+    this._container.appendChild(this._nextBox);
+
+    this._boxWidth = this._curBox.getBoundingClientRect().width; // cache width
+  },
+
+  /**
+   * Removes the boxes.
+   */
+  _removeBoxes: function HSA__removeBoxes() {
+    this._curBox = null;
+    this._prevBox = null;
+    this._nextBox = null;
+    if (this._container)
+      this._container.parentNode.removeChild(this._container);
+    this._container = null;
+    this._boxWidth = -1;
+  },
+
+  /**
+   * Creates an element with a given identifier and tag name.
+   *
+   * @param aID
+   *        An identifier to create the element with.
+   * @param aTagName
+   *        The name of the tag to create the element for.
+   * @return the newly created element.
+   */
+  _createElement: function HSA__createElement(aID, aTagName) {
+    let XULNS = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
+    let element = document.createElementNS(XULNS, aTagName);
+    element.id = aID;
+    return element;
+  },
+
+  /**
+   * Moves a given box to a given X coordinate position.
+   *
+   * @param aBox
+   *        The box element to position.
+   * @param aPosition
+   *        The position (in X coordinates) to move the box element to.
+   */
+  _positionBox: function HSA__positionBox(aBox, aPosition) {
+    aBox.style.transform = "translateX(" + this._boxWidth * aPosition + "px)";
+  },
+
+  /**
+   * Takes a snapshot of the page the browser is currently on.
+   */
+  _takeSnapshot: function HSA__takeSnapshot() {
+    if ((this._maxSnapshots < 1) ||
+        (gBrowser.webNavigation.sessionHistory.index < 0))
+      return;
+
+    let browser = gBrowser.selectedBrowser;
+    let r = browser.getBoundingClientRect();
+    let canvas = document.createElementNS("http://www.w3.org/1999/xhtml",
+                                          "canvas");
+    canvas.mozOpaque = true;
+    canvas.width = r.width;
+    canvas.height = r.height;
+    let ctx = canvas.getContext("2d");
+    let zoom = browser.markupDocumentViewer.fullZoom;
+    ctx.scale(zoom, zoom);
+    ctx.drawWindow(browser.contentWindow, 0, 0, r.width, r.height, "white",
+                   ctx.DRAWWINDOW_DO_NOT_FLUSH | ctx.DRAWWINDOW_DRAW_VIEW |
+                   ctx.DRAWWINDOW_ASYNC_DECODE_IMAGES |
+                   ctx.DRAWWINDOW_USE_WIDGET_LAYERS);
+
+    this._installCurrentPageSnapshot(canvas);
+    this._assignSnapshotToCurrentBrowser(canvas);
+  },
+
+  /**
+   * Retrieves the maximum number of snapshots that should be kept in memory.
+   * This limit is a global limit and is valid across all open tabs.
+   */
+  _getMaxSnapshots: function HSA__getMaxSnapshots() {
+    return gPrefService.getIntPref("browser.snapshots.limit");
+  },
+
+  /**
+   * Adds a snapshot to the list and initiates the compression of said snapshot.
+   * Once the compression is completed, it will replace the uncompressed
+   * snapshot in the list.
+   *
+   * @param aCanvas
+   *        The snapshot to add to the list and compress.
+   */
+  _assignSnapshotToCurrentBrowser:
+  function HSA__assignSnapshotToCurrentBrowser(aCanvas) {
+    let browser = gBrowser.selectedBrowser;
+    let currIndex = browser.webNavigation.sessionHistory.index;
+
+    this._removeTrackedSnapshot(currIndex, browser);
+    this._addSnapshotRefToArray(currIndex, browser);
+
+    if (!("snapshots" in browser))
+      browser.snapshots = [];
+    let snapshots = browser.snapshots;
+    // Temporarily store the canvas as the compressed snapshot.
+    // This avoids a blank page if the user swipes quickly
+    // between pages before the compression could complete.
+    snapshots[currIndex] = aCanvas;
+
+    // Kick off snapshot compression.
+    aCanvas.toBlob(function(aBlob) {
+        snapshots[currIndex] = aBlob;
+      }, "image/png"
+    );
+  },
+
+  /**
+   * Removes a snapshot identified by the browser and index in the array of
+   * snapshots for that browser, if present. If no snapshot could be identified
+   * the method simply returns without taking any action. If aIndex is negative,
+   * all snapshots for a particular browser will be removed.
+   *
+   * @param aIndex
+   *        The index in history of the new snapshot, or negative value if all
+   *        snapshots for a browser should be removed.
+   * @param aBrowser
+   *        The browser the new snapshot was taken in.
+   */
+  _removeTrackedSnapshot: function HSA__removeTrackedSnapshot(aIndex, aBrowser) {
+    let arr = this._trackedSnapshots;
+    let requiresExactIndexMatch = aIndex >= 0;
+    for (let i = 0; i < arr.length; i++) {
+      if ((arr[i].browser == aBrowser) &&
+          (aIndex < 0 || aIndex == arr[i].index)) {
+        delete aBrowser.snapshots[arr[i].index];
+        arr.splice(i, 1);
+        if (requiresExactIndexMatch)
+          return; // Found and removed the only element.
+        i--; // Make sure to revisit the index that we just removed an
+             // element at.
+      }
+    }
+  },
+
+  /**
+   * Adds a new snapshot reference for a given index and browser to the array
+   * of references to tracked snapshots.
+   *
+   * @param aIndex
+   *        The index in history of the new snapshot.
+   * @param aBrowser
+   *        The browser the new snapshot was taken in.
+   */
+  _addSnapshotRefToArray:
+  function HSA__addSnapshotRefToArray(aIndex, aBrowser) {
+    let id = { index: aIndex,
+               browser: aBrowser };
+    let arr = this._trackedSnapshots;
+    arr.unshift(id);
+
+    while (arr.length > this._maxSnapshots) {
+      let lastElem = arr[arr.length - 1];
+      delete lastElem.browser.snapshots[lastElem.index];
+      arr.splice(-1, 1);
+    }
+  },
+
+  /**
+   * Converts a compressed blob to an Image object. In some situations
+   * (especially during fast swiping) aBlob may still be a canvas, not a
+   * compressed blob. In this case, we simply return the canvas.
+   *
+   * @param aBlob
+   *        The compressed blob to convert, or a canvas if a blob compression
+   *        couldn't complete before this method was called.
+   * @return A new Image object representing the converted blob.
+   */
+  _convertToImg: function HSA__convertToImg(aBlob) {
+    if (!aBlob)
+      return null;
+
+    // Return aBlob if it's still a canvas and not a compressed blob yet.
+    if (aBlob instanceof HTMLCanvasElement)
+      return aBlob;
+
+    let img = new Image();
+    let url = URL.createObjectURL(aBlob);
+    img.onload = function() {
+      URL.revokeObjectURL(url);
+    };
+    img.src = url;
+    return img;
+  },
+
+  /**
+   * Sets the snapshot of the current page to the snapshot passed as parameter,
+   * or to the one previously stored for the current index in history if the
+   * parameter is null.
+   *
+   * @param aCanvas
+   *        The snapshot to set the current page to. If this parameter is null,
+   *        the previously stored snapshot for this index (if any) will be used.
+   */
+  _installCurrentPageSnapshot:
+  function HSA__installCurrentPageSnapshot(aCanvas) {
+    let currSnapshot = aCanvas;
+    if (!currSnapshot) {
+      let snapshots = gBrowser.selectedBrowser.snapshots || {};
+      let currIndex = this._historyIndex;
+      if (currIndex in snapshots)
+        currSnapshot = this._convertToImg(snapshots[currIndex]);
+    }
+    document.mozSetImageElement("historySwipeAnimationCurrentPageSnapshot",
+                                  currSnapshot);
+  },
+
+  /**
+   * Sets the snapshots of the previous and next pages to the snapshots
+   * previously stored for their respective indeces.
+   */
+  _installPrevAndNextSnapshots:
+  function HSA__installPrevAndNextSnapshots() {
+    let snapshots = gBrowser.selectedBrowser.snapshots || [];
+    let currIndex = this._historyIndex;
+    let prevIndex = currIndex - 1;
+    let prevSnapshot = null;
+    if (prevIndex in snapshots)
+      prevSnapshot = this._convertToImg(snapshots[prevIndex]);
+    document.mozSetImageElement("historySwipeAnimationPreviousPageSnapshot",
+                                prevSnapshot);
+
+    let nextIndex = currIndex + 1;
+    let nextSnapshot = null;
+    if (nextIndex in snapshots)
+      nextSnapshot = this._convertToImg(snapshots[nextIndex]);
+    document.mozSetImageElement("historySwipeAnimationNextPageSnapshot",
+                                nextSnapshot);
+  },
+};