Master merge

This merges master into release to replace Redwood.

# Conflicts:
#	CLOBBER
#	build/moz.configure/old.configure
#	config/milestone.txt
#	config/moz.build
#	config/system-headers
#	dom/abort/AbortController.cpp
#	dom/abort/AbortController.h
#	dom/abort/AbortSignal.cpp
#	dom/abort/AbortSignal.h
#	dom/abort/moz.build
#	dom/abort/tests/moz.build
#	dom/animation/KeyframeEffect.cpp
#	dom/base/CustomElementRegistry.cpp
#	dom/base/DocGroup.cpp
#	dom/base/ResizeObserverController.cpp
#	dom/base/ResizeObserverController.h
#	dom/base/nsContentUtils.cpp
#	dom/base/nsContentUtils.h
#	dom/base/nsDocument.cpp
#	dom/base/nsIDocument.h
#	dom/fetch/FetchObserver.cpp
#	dom/fetch/FetchObserver.h
#	dom/heapsnapshot/AutoMemMap.cpp
#	dom/heapsnapshot/AutoMemMap.h
#	dom/heapsnapshot/CoreDump.proto
#	dom/heapsnapshot/HeapSnapshot.cpp
#	dom/heapsnapshot/HeapSnapshotTempFileHelperChild.h
#	dom/heapsnapshot/HeapSnapshotTempFileHelperParent.cpp
#	dom/heapsnapshot/HeapSnapshotTempFileHelperParent.h
#	dom/heapsnapshot/PHeapSnapshotTempFileHelper.ipdl
#	dom/heapsnapshot/moz.build
#	dom/heapsnapshot/tests/gtest/moz.build
#	dom/html/nsGenericHTMLElement.h
#	dom/media/platforms/PlatformDecoderModule.h
#	dom/media/platforms/moz.build
#	dom/script/ModuleLoadRequest.cpp
#	dom/script/ModuleLoadRequest.h
#	dom/script/ModuleScript.cpp
#	dom/script/ModuleScript.h
#	dom/script/ScriptElement.cpp
#	dom/script/ScriptElement.h
#	dom/script/ScriptLoadHandler.cpp
#	dom/script/ScriptLoadHandler.h
#	dom/script/ScriptLoader.cpp
#	dom/script/ScriptLoader.h
#	dom/script/ScriptSettings.cpp
#	dom/script/ScriptSettings.h
#	dom/script/nsIScriptElement.h
#	dom/script/nsIScriptLoaderObserver.idl
#	dom/webidl/HTMLLinkElement.webidl
#	gfx/gl/moz.build
#	gfx/graphite2/src/moz.build
#	gfx/layers/moz.build
#	js/ductwork/inspector/moz.build
#	js/ductwork/moz.build
#	js/src/gc/Heap.h
#	js/src/moz.build
#	js/src/vm/UnboxedObject-inl.h
#	js/src/vm/UnboxedObject.cpp
#	js/src/vm/UnboxedObject.h
#	layout/base/crashtests/crashtests.list
#	layout/build/moz.build
#	layout/generic/AspectRatio.h
#	layout/generic/crashtests/crashtests.list
#	layout/reftests/bidi/reftest-stylo.list
#	layout/reftests/reftest-stylo.list
#	layout/reftests/table-bordercollapse/reftest.list
#	layout/reftests/writing-mode/reftest-stylo.list
#	layout/style/StyleSheet.cpp
#	layout/style/nsRuleNode.cpp
#	layout/style/nsStyleStruct.cpp
#	layout/style/nsStyleStruct.h
#	modules/libpref/init/all.js
#	nsprpub/pr/src/linking/prlink.c
#	parser/html/java/htmlparser/src/nu/validator/htmlparser/impl/AttributeName.java
#	parser/html/java/htmlparser/src/nu/validator/htmlparser/impl/ElementName.java
#	parser/html/nsHtml5AtomList.h
#	parser/html/nsHtml5AttributeName.cpp
#	parser/html/nsHtml5AttributeName.h
#	parser/html/nsHtml5ElementName.cpp
#	parser/html/nsHtml5ElementName.h
#	parser/html/nsHtml5TreeBuilderCppSupplement.h
#	parser/htmlparser/nsElementTable.cpp
#	parser/htmlparser/nsHTMLTagList.h
#	security/nss/lib/nss/nss.h
#	security/nss/lib/softoken/pkcs11.c
#	security/nss/lib/softoken/softkver.h
#	security/nss/lib/util/nssutil.h
#	testing/web-platform/tests/tools/html5lib/html5lib/html5parser.py
#	testing/web-platform/tests/tools/html5lib/html5lib/treebuilders/_base.py
#	toolkit/modules/AppConstants.jsm

54 files changed, 135 insertions, 109 deletions

diff --git a/widget/BasicEvents.h b/widget/BasicEvents.h
index 960cb67c6..0ce0f587d 100644
--- a/widget/BasicEvents.h
+++ b/widget/BasicEvents.h
@@ -25,6 +25,8 @@ struct ParamTraits;
 
 namespace mozilla {
 
+class EventTargetChainItem;
+
 /******************************************************************************
  * mozilla::BaseEventFlags
  *
@@ -350,6 +352,7 @@ protected:
     , mRefPoint(0, 0)
     , mLastRefPoint(0, 0)
     , mSpecifiedEventType(nullptr)
+    , mPath(nullptr)
   {
     MOZ_COUNT_CTOR(WidgetEvent);
     mFlags.Clear();
@@ -361,6 +364,7 @@ protected:
 
   WidgetEvent()
     : WidgetEventTime()
+    , mPath(nullptr)
   {
     MOZ_COUNT_CTOR(WidgetEvent);
   }
@@ -419,6 +423,11 @@ public:
   nsCOMPtr<dom::EventTarget> mCurrentTarget;
   nsCOMPtr<dom::EventTarget> mOriginalTarget;
 
+  /// The possible related target
+  nsCOMPtr<dom::EventTarget> mRelatedTarget;
+
+  nsTArray<EventTargetChainItem>* mPath;
+
   dom::EventTarget* GetDOMEventTarget() const;
   dom::EventTarget* GetCurrentDOMEventTarget() const;
   dom::EventTarget* GetOriginalDOMEventTarget() const;
@@ -436,6 +445,7 @@ public:
     mTarget = aCopyTargets ? aEvent.mTarget : nullptr;
     mCurrentTarget = aCopyTargets ? aEvent.mCurrentTarget : nullptr;
     mOriginalTarget = aCopyTargets ? aEvent.mOriginalTarget : nullptr;
+    mRelatedTarget = aCopyTargets ? aEvent.mRelatedTarget : nullptr;
   }
 
   /**
diff --git a/widget/ContentEvents.h b/widget/ContentEvents.h
index be64b7beb..09d4d9928 100644
--- a/widget/ContentEvents.h
+++ b/widget/ContentEvents.h
@@ -212,9 +212,6 @@ public:
     return result;
   }
 
-  /// The possible related target
-  nsCOMPtr<dom::EventTarget> mRelatedTarget;
-
   bool mFromRaise;
   bool mIsRefocus;
 
@@ -222,7 +219,6 @@ public:
   {
     AssignUIEventData(aEvent, aCopyTargets);
 
-    mRelatedTarget = aCopyTargets ? aEvent.mRelatedTarget : nullptr;
     mFromRaise = aEvent.mFromRaise;
     mIsRefocus = aEvent.mIsRefocus;
   }
diff --git a/widget/FontRange.h b/widget/FontRange.h
index 15cb4a01d..ef7b601e9 100644
--- a/widget/FontRange.h
+++ b/widget/FontRange.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/MouseEvents.h b/widget/MouseEvents.h
index 442ac41e8..4b8ff44ce 100644
--- a/widget/MouseEvents.h
+++ b/widget/MouseEvents.h
@@ -110,9 +110,6 @@ public:
     MOZ_CRASH("WidgetMouseEventBase must not be most-subclass");
   }
 
-  /// The possible related target
-  nsCOMPtr<nsISupports> relatedTarget;
-
   enum buttonType
   {
     eLeftButton   = 0,
@@ -162,7 +159,6 @@ public:
   {
     AssignInputEventData(aEvent, aCopyTargets);
 
-    relatedTarget = aCopyTargets ? aEvent.relatedTarget : nullptr;
     button = aEvent.button;
     buttons = aEvent.buttons;
     pressure = aEvent.pressure;
diff --git a/widget/NativeKeyToDOMCodeName.h b/widget/NativeKeyToDOMCodeName.h
index 159b0773c..74f2ed1f4 100644
--- a/widget/NativeKeyToDOMCodeName.h
+++ b/widget/NativeKeyToDOMCodeName.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/NativeKeyToDOMKeyName.h b/widget/NativeKeyToDOMKeyName.h
index ce1e3c3a4..25dafff6f 100644
--- a/widget/NativeKeyToDOMKeyName.h
+++ b/widget/NativeKeyToDOMKeyName.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/PCompositorWidget.ipdl b/widget/PCompositorWidget.ipdl
index f8ffd8dff..4c83d92fa 100644
--- a/widget/PCompositorWidget.ipdl
+++ b/widget/PCompositorWidget.ipdl
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=99: */
 /* 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/. */
diff --git a/widget/PlatformWidgetTypes.ipdlh b/widget/PlatformWidgetTypes.ipdlh
index 26933f8de..af2579155 100644
--- a/widget/PlatformWidgetTypes.ipdlh
+++ b/widget/PlatformWidgetTypes.ipdlh
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=99: */
 /* 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/. */
diff --git a/widget/ScreenProxy.cpp b/widget/ScreenProxy.cpp
index 462dd7476..d8abbad01 100644
--- a/widget/ScreenProxy.cpp
+++ b/widget/ScreenProxy.cpp
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil; tab-width: 2; -*- */
-/* vim: set sw=4 ts=8 et tw=80 : */
 /* 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/. */
diff --git a/widget/ScreenProxy.h b/widget/ScreenProxy.h
index 22e78c36d..6fa1283ca 100644
--- a/widget/ScreenProxy.h
+++ b/widget/ScreenProxy.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil; tab-width: 2; -*- */
-/* vim: set sw=4 ts=8 et tw=80 : */
 /* 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/. */
diff --git a/widget/cocoa/SwipeTracker.h b/widget/cocoa/SwipeTracker.h
index b5eb2a481..78940d15c 100644
--- a/widget/cocoa/SwipeTracker.h
+++ b/widget/cocoa/SwipeTracker.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/cocoa/SwipeTracker.mm b/widget/cocoa/SwipeTracker.mm
index 9c06ee0c3..51169171a 100644
--- a/widget/cocoa/SwipeTracker.mm
+++ b/widget/cocoa/SwipeTracker.mm
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/cocoa/TextInputHandler.h b/widget/cocoa/TextInputHandler.h
index de7c77593..86da354ab 100644
--- a/widget/cocoa/TextInputHandler.h
+++ b/widget/cocoa/TextInputHandler.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=2 sw=2 et tw=80: */
 /* 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/. */
diff --git a/widget/cocoa/TextInputHandler.mm b/widget/cocoa/TextInputHandler.mm
index 39965d013..348d99ab6 100644
--- a/widget/cocoa/TextInputHandler.mm
+++ b/widget/cocoa/TextInputHandler.mm
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=2 sw=2 et tw=80: */
 /* 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/. */
diff --git a/widget/cocoa/VibrancyManager.h b/widget/cocoa/VibrancyManager.h
index cae57a269..04b1ad1cd 100644
--- a/widget/cocoa/VibrancyManager.h
+++ b/widget/cocoa/VibrancyManager.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/cocoa/VibrancyManager.mm b/widget/cocoa/VibrancyManager.mm
index 93a774254..d02338eb6 100644
--- a/widget/cocoa/VibrancyManager.mm
+++ b/widget/cocoa/VibrancyManager.mm
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/cocoa/ViewRegion.h b/widget/cocoa/ViewRegion.h
index a8efccaff..9ff7e6d09 100644
--- a/widget/cocoa/ViewRegion.h
+++ b/widget/cocoa/ViewRegion.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/cocoa/ViewRegion.mm b/widget/cocoa/ViewRegion.mm
index b3605caa2..455d54fda 100644
--- a/widget/cocoa/ViewRegion.mm
+++ b/widget/cocoa/ViewRegion.mm
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/cocoa/moz.build b/widget/cocoa/moz.build
index 7c995d900..c4f887297 100644
--- a/widget/cocoa/moz.build
+++ b/widget/cocoa/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.
diff --git a/widget/cocoa/nsCocoaWindow.mm b/widget/cocoa/nsCocoaWindow.mm
index b141e80b0..a437504fd 100644
--- a/widget/cocoa/nsCocoaWindow.mm
+++ b/widget/cocoa/nsCocoaWindow.mm
@@ -1,5 +1,4 @@
 /* -*- Mode: Objective-C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/cocoa/nsNativeThemeCocoa.mm b/widget/cocoa/nsNativeThemeCocoa.mm
index f93e40f7b..056c453f2 100644
--- a/widget/cocoa/nsNativeThemeCocoa.mm
+++ b/widget/cocoa/nsNativeThemeCocoa.mm
@@ -2279,6 +2279,12 @@ IsHiDPIContext(nsPresContext* aContext)
     2 * aContext->DeviceContext()->AppUnitsPerDevPixelAtUnitFullZoom();
 }
 
+static bool
+IsScrollbarWidthThin(nsIFrame* aFrame)
+{
+  return aFrame->StyleUserInterface()->mScrollbarWidth == StyleScrollbarWidth::Thin;
+}
+
 NS_IMETHODIMP
 nsNativeThemeCocoa::DrawWidgetBackground(nsRenderingContext* aContext,
                                          nsIFrame* aFrame,
@@ -3392,9 +3398,10 @@ nsNativeThemeCocoa::GetMinimumWidgetSize(nsPresContext* aPresContext,
       // Find our parent scrollbar frame in order to find out whether we're in
       // a small or a large scrollbar.
       nsIFrame *scrollbarFrame = GetParentScrollbarFrame(aFrame);
-      if (!scrollbarFrame)
+      if (!scrollbarFrame) {
         return NS_ERROR_FAILURE;
-
+      }
+      
       bool isSmall = (scrollbarFrame->StyleDisplay()->mAppearance == NS_THEME_SCROLLBAR_SMALL);
       bool isHorizontal = (aWidgetType == NS_THEME_SCROLLBARTHUMB_HORIZONTAL);
       int32_t& minSize = isHorizontal ? aResult->width : aResult->height;
@@ -3419,6 +3426,9 @@ nsNativeThemeCocoa::GetMinimumWidgetSize(nsPresContext* aPresContext,
         else {
           aResult->SizeTo(16, 16);
         }
+        if (IsScrollbarWidthThin(aFrame)) {
+          aResult->SizeTo(8, 8);
+        }
         break;
       }
 
@@ -3435,6 +3445,9 @@ nsNativeThemeCocoa::GetMinimumWidgetSize(nsPresContext* aPresContext,
                             kThemeMetricScrollBarWidth;
       SInt32 scrollbarWidth = 0;
       ::GetThemeMetric(themeMetric, &scrollbarWidth);
+      if (IsScrollbarWidthThin(aFrame)) {
+        scrollbarWidth /= 2;
+      }
       aResult->SizeTo(scrollbarWidth, scrollbarWidth);
       break;
     }
@@ -3467,22 +3480,26 @@ nsNativeThemeCocoa::GetMinimumWidgetSize(nsPresContext* aPresContext,
     case NS_THEME_SCROLLBARBUTTON_LEFT:
     case NS_THEME_SCROLLBARBUTTON_RIGHT:
     {
-      nsIFrame *scrollbarFrame = GetParentScrollbarFrame(aFrame);
-      if (!scrollbarFrame) return NS_ERROR_FAILURE;
-
-      // Since there is no NS_THEME_SCROLLBARBUTTON_UP_SMALL we need to ask the parent what appearance style it has.
-      int32_t themeMetric = (scrollbarFrame->StyleDisplay()->mAppearance == NS_THEME_SCROLLBAR_SMALL) ?
-                            kThemeMetricSmallScrollBarWidth :
-                            kThemeMetricScrollBarWidth;
-      SInt32 scrollbarWidth = 0;
-      ::GetThemeMetric(themeMetric, &scrollbarWidth);
-
-      // It seems that for both sizes of scrollbar, the buttons are one pixel "longer".
-      if (aWidgetType == NS_THEME_SCROLLBARBUTTON_LEFT || aWidgetType == NS_THEME_SCROLLBARBUTTON_RIGHT)
-        aResult->SizeTo(scrollbarWidth+1, scrollbarWidth);
-      else
-        aResult->SizeTo(scrollbarWidth, scrollbarWidth+1);
- 
+      if (!IsScrollbarWidthThin(aFrame)) {
+        // Get scrollbar button metrics from the system, except in the case of
+        // thin scrollbars, where we leave them at 0 (collapse)
+
+        nsIFrame *scrollbarFrame = GetParentScrollbarFrame(aFrame);
+        if (!scrollbarFrame) return NS_ERROR_FAILURE;
+
+        // Since there is no NS_THEME_SCROLLBARBUTTON_UP_SMALL we need to ask the parent what appearance style it has.
+        int32_t themeMetric = (scrollbarFrame->StyleDisplay()->mAppearance == NS_THEME_SCROLLBAR_SMALL) ?
+                              kThemeMetricSmallScrollBarWidth :
+                              kThemeMetricScrollBarWidth;
+        SInt32 scrollbarWidth = 0;
+        ::GetThemeMetric(themeMetric, &scrollbarWidth);
+
+        // It seems that for both sizes of scrollbar, the buttons are one pixel "longer".
+        if (aWidgetType == NS_THEME_SCROLLBARBUTTON_LEFT || aWidgetType == NS_THEME_SCROLLBARBUTTON_RIGHT)
+          aResult->SizeTo(scrollbarWidth+1, scrollbarWidth);
+        else
+          aResult->SizeTo(scrollbarWidth, scrollbarWidth+1);
+      }
       *aIsOverridable = false;
       break;
     }
diff --git a/widget/gtk/IMContextWrapper.cpp b/widget/gtk/IMContextWrapper.cpp
index 58d7a3681..441bb7bbf 100644
--- a/widget/gtk/IMContextWrapper.cpp
+++ b/widget/gtk/IMContextWrapper.cpp
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
-/* vim: set ts=4 et sw=4 tw=80: */
 /* 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/. */
diff --git a/widget/gtk/PCompositorWidget.ipdl b/widget/gtk/PCompositorWidget.ipdl
index 178fe78e4..fe98fc116 100644
--- a/widget/gtk/PCompositorWidget.ipdl
+++ b/widget/gtk/PCompositorWidget.ipdl
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=99: */
 /* 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/. */
diff --git a/widget/gtk/PlatformWidgetTypes.ipdlh b/widget/gtk/PlatformWidgetTypes.ipdlh
index 145d39546..cab34a4cc 100644
--- a/widget/gtk/PlatformWidgetTypes.ipdlh
+++ b/widget/gtk/PlatformWidgetTypes.ipdlh
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=99: */
 /* 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/. */
diff --git a/widget/gtk/WidgetStyleCache.cpp b/widget/gtk/WidgetStyleCache.cpp
index f35a451aa..7296146f9 100644
--- a/widget/gtk/WidgetStyleCache.cpp
+++ b/widget/gtk/WidgetStyleCache.cpp
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/gtk/WidgetStyleCache.h b/widget/gtk/WidgetStyleCache.h
index 2cbb5f960..fbdfa9349 100644
--- a/widget/gtk/WidgetStyleCache.h
+++ b/widget/gtk/WidgetStyleCache.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/gtk/moz.build b/widget/gtk/moz.build
index 8d621c0a0..7c802a3c1 100644
--- a/widget/gtk/moz.build
+++ b/widget/gtk/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.
diff --git a/widget/gtk/mozgtk/gtk2/moz.build b/widget/gtk/mozgtk/gtk2/moz.build
index d07fd06df..db7bb0972 100644
--- a/widget/gtk/mozgtk/gtk2/moz.build
+++ b/widget/gtk/mozgtk/gtk2/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.
diff --git a/widget/gtk/mozgtk/gtk3/moz.build b/widget/gtk/mozgtk/gtk3/moz.build
index 4e9379565..ec9a5ef46 100644
--- a/widget/gtk/mozgtk/gtk3/moz.build
+++ b/widget/gtk/mozgtk/gtk3/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.
diff --git a/widget/gtk/mozgtk/moz.build b/widget/gtk/mozgtk/moz.build
index 528e2e9d0..43f94aabf 100644
--- a/widget/gtk/mozgtk/moz.build
+++ b/widget/gtk/mozgtk/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.
diff --git a/widget/gtk/mozgtk/stub/moz.build b/widget/gtk/mozgtk/stub/moz.build
index 1a8e21001..7713bfaaf 100644
--- a/widget/gtk/mozgtk/stub/moz.build
+++ b/widget/gtk/mozgtk/stub/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.
diff --git a/widget/gtk/nsDragService.cpp b/widget/gtk/nsDragService.cpp
index 15b4eeffa..aa5ee2c7a 100644
--- a/widget/gtk/nsDragService.cpp
+++ b/widget/gtk/nsDragService.cpp
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
-/* vim: set ts=4 et sw=4 tw=80: */
 /* 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/. */
diff --git a/widget/gtk/nsDragService.h b/widget/gtk/nsDragService.h
index 90c113106..f3027eeea 100644
--- a/widget/gtk/nsDragService.h
+++ b/widget/gtk/nsDragService.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
-/* vim: set ts=4 et sw=4 tw=80: */
 /* 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/. */
diff --git a/widget/gtk/nsNativeThemeGTK.cpp b/widget/gtk/nsNativeThemeGTK.cpp
index 89b8ab7dc..cb4e7debf 100644
--- a/widget/gtk/nsNativeThemeGTK.cpp
+++ b/widget/gtk/nsNativeThemeGTK.cpp
@@ -1098,6 +1098,12 @@ nsNativeThemeGTK::GetExtraSizeForWidget(nsIFrame* aFrame, uint8_t aWidgetType,
   return true;
 }
 
+static bool
+IsScrollbarWidthThin(nsIFrame* aFrame)
+{
+  return aFrame->StyleUserInterface()->mScrollbarWidth == StyleScrollbarWidth::Thin;
+}
+
 NS_IMETHODIMP
 nsNativeThemeGTK::DrawWidgetBackground(nsRenderingContext* aContext,
                                        nsIFrame* aFrame,
@@ -1419,32 +1425,39 @@ nsNativeThemeGTK::GetMinimumWidgetSize(nsPresContext* aPresContext,
     case NS_THEME_SCROLLBARBUTTON_UP:
     case NS_THEME_SCROLLBARBUTTON_DOWN:
       {
-        if (gtk_check_version(3,20,0) == nullptr) {
-          moz_gtk_get_widget_min_size(MOZ_GTK_SCROLLBAR_BUTTON,
-                                      &(aResult->width), &(aResult->height));
-        } else {
-          MozGtkScrollbarMetrics metrics;
-          moz_gtk_get_scrollbar_metrics(&metrics);
+        if (!IsScrollbarWidthThin(aFrame)) {
+          // Get scrollbar button metrics from the system, except in the case of
+          // thin scrollbars, where we leave them at 0 (collapse)
+          if (gtk_check_version(3,20,0) == nullptr) {
+            moz_gtk_get_widget_min_size(MOZ_GTK_SCROLLBAR_BUTTON,
+                                        &(aResult->width), &(aResult->height));
+          } else {
+            MozGtkScrollbarMetrics metrics;
+            moz_gtk_get_scrollbar_metrics(&metrics);
 
-          aResult->width = metrics.slider_width;
-          aResult->height = metrics.stepper_size;
+            aResult->width = metrics.slider_width;
+            aResult->height = metrics.stepper_size;
+          }
         }
-
         *aIsOverridable = false;
       }
       break;
     case NS_THEME_SCROLLBARBUTTON_LEFT:
     case NS_THEME_SCROLLBARBUTTON_RIGHT:
       {
-        if (gtk_check_version(3,20,0) == nullptr) {
-          moz_gtk_get_widget_min_size(MOZ_GTK_SCROLLBAR_BUTTON,
-                                      &(aResult->width), &(aResult->height));
-        } else {
-          MozGtkScrollbarMetrics metrics;
-          moz_gtk_get_scrollbar_metrics(&metrics);
+        if (!IsScrollbarWidthThin(aFrame)) {
+          // Get scrollbar button metrics from the system, except in the case of
+          // thin scrollbars, where we leave them at 0 (collapse)
+          if (gtk_check_version(3,20,0) == nullptr) {
+            moz_gtk_get_widget_min_size(MOZ_GTK_SCROLLBAR_BUTTON,
+                                        &(aResult->width), &(aResult->height));
+          } else {
+            MozGtkScrollbarMetrics metrics;
+            moz_gtk_get_scrollbar_metrics(&metrics);
 
-          aResult->width = metrics.stepper_size;
-          aResult->height = metrics.slider_width;
+            aResult->width = metrics.stepper_size;
+            aResult->height = metrics.slider_width;
+          }
         }
         *aIsOverridable = false;
       }
@@ -1514,6 +1527,24 @@ nsNativeThemeGTK::GetMinimumWidgetSize(nsPresContext* aPresContext,
     }
     break;
     case NS_THEME_SCROLLBARTHUMB_VERTICAL:
+      {
+        if (gtk_check_version(3,20,0) == nullptr) {
+          moz_gtk_get_widget_min_size(NativeThemeToGtkTheme(aWidgetType, aFrame),
+                                      &(aResult->width), &(aResult->height));
+        } else {
+          MozGtkScrollbarMetrics metrics;
+          moz_gtk_get_scrollbar_metrics(&metrics);
+
+          aResult->width = metrics.slider_width;
+          aResult->height = metrics.min_slider_size;
+        }
+        if (IsScrollbarWidthThin(aFrame)) {
+          // If thin scrollbars, divide the thickness by 3
+          aResult->width /= 3;
+        }
+        *aIsOverridable = false;
+      }
+      break;
     case NS_THEME_SCROLLBARTHUMB_HORIZONTAL:
       {
         if (gtk_check_version(3,20,0) == nullptr) {
@@ -1523,13 +1554,12 @@ nsNativeThemeGTK::GetMinimumWidgetSize(nsPresContext* aPresContext,
           MozGtkScrollbarMetrics metrics;
           moz_gtk_get_scrollbar_metrics(&metrics);
 
-          if (aWidgetType == NS_THEME_SCROLLBARTHUMB_VERTICAL) {
-            aResult->width = metrics.slider_width;
-            aResult->height = metrics.min_slider_size;
-          } else {
-            aResult->height = metrics.slider_width;
-            aResult->width = metrics.min_slider_size;
-          }
+          aResult->height = metrics.slider_width;
+          aResult->width = metrics.min_slider_size;
+        }
+        if (IsScrollbarWidthThin(aFrame)) {
+          // If thin scrollbars, divide the thickness by 3
+          aResult->height /= 3;
         }
         *aIsOverridable = false;
       }
diff --git a/widget/gtkxtbin/gtk2xtbin.c b/widget/gtkxtbin/gtk2xtbin.c
index 189478bad..01e4b0bdd 100644
--- a/widget/gtkxtbin/gtk2xtbin.c
+++ b/widget/gtkxtbin/gtk2xtbin.c
@@ -1,5 +1,4 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
- * vim: set expandtab shiftwidth=2 tabstop=2: */
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
  
 /* 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
diff --git a/widget/gtkxtbin/gtk2xtbin.h b/widget/gtkxtbin/gtk2xtbin.h
index 60b3a0b34..cffb752e6 100644
--- a/widget/gtkxtbin/gtk2xtbin.h
+++ b/widget/gtkxtbin/gtk2xtbin.h
@@ -1,5 +1,4 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
- * vim: set expandtab shiftwidth=2 tabstop=2: */
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
  
 /* 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
diff --git a/widget/gtkxtbin/moz.build b/widget/gtkxtbin/moz.build
index 070aa5777..41b867c3c 100644
--- a/widget/gtkxtbin/moz.build
+++ b/widget/gtkxtbin/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.
diff --git a/widget/gtkxtbin/xembed.h b/widget/gtkxtbin/xembed.h
index 605c128aa..5a5390091 100644
--- a/widget/gtkxtbin/xembed.h
+++ b/widget/gtkxtbin/xembed.h
@@ -1,5 +1,4 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
- * vim: set expandtab shiftwidth=2 tabstop=2: */
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
  
 /* 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
diff --git a/widget/moz.build b/widget/moz.build
index 3a52805b0..c72b2066c 100644
--- a/widget/moz.build
+++ b/widget/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.
diff --git a/widget/nsBaseWidget.cpp b/widget/nsBaseWidget.cpp
index c6ec3a406..d3cdf72cf 100644
--- a/widget/nsBaseWidget.cpp
+++ b/widget/nsBaseWidget.cpp
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/nsDeviceContextSpecProxy.cpp b/widget/nsDeviceContextSpecProxy.cpp
index dafbf1549..df0927237 100644
--- a/widget/nsDeviceContextSpecProxy.cpp
+++ b/widget/nsDeviceContextSpecProxy.cpp
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/nsDeviceContextSpecProxy.h b/widget/nsDeviceContextSpecProxy.h
index adde3cc11..df065fc7b 100644
--- a/widget/nsDeviceContextSpecProxy.h
+++ b/widget/nsDeviceContextSpecProxy.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/uikit/moz.build b/widget/uikit/moz.build
index 50aed405b..2c6c188de 100644
--- a/widget/uikit/moz.build
+++ b/widget/uikit/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.
diff --git a/widget/windows/InkCollector.cpp b/widget/windows/InkCollector.cpp
index 3268fe95b..9871b9661 100644
--- a/widget/windows/InkCollector.cpp
+++ b/widget/windows/InkCollector.cpp
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
-* vim: set ts=2 sw=2 et tw=78:
 * 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/.
diff --git a/widget/windows/InkCollector.h b/widget/windows/InkCollector.h
index 9570eea2a..b466ef05b 100644
--- a/widget/windows/InkCollector.h
+++ b/widget/windows/InkCollector.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
-* vim: set ts=2 sw=2 et tw=78:
 * 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/.
diff --git a/widget/windows/PCompositorWidget.ipdl b/widget/windows/PCompositorWidget.ipdl
index 4805c95a4..1a9c65e12 100644
--- a/widget/windows/PCompositorWidget.ipdl
+++ b/widget/windows/PCompositorWidget.ipdl
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=99: */
 /* 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/. */
diff --git a/widget/windows/PlatformWidgetTypes.ipdlh b/widget/windows/PlatformWidgetTypes.ipdlh
index aad9cf395..1ebc54769 100644
--- a/widget/windows/PlatformWidgetTypes.ipdlh
+++ b/widget/windows/PlatformWidgetTypes.ipdlh
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=99: */
 /* 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/. */
diff --git a/widget/windows/WinMouseScrollHandler.cpp b/widget/windows/WinMouseScrollHandler.cpp
index e157b1be2..ef6b92ea4 100644
--- a/widget/windows/WinMouseScrollHandler.cpp
+++ b/widget/windows/WinMouseScrollHandler.cpp
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/windows/WinMouseScrollHandler.h b/widget/windows/WinMouseScrollHandler.h
index 5d8c58ba0..7ebd551ea 100644
--- a/widget/windows/WinMouseScrollHandler.h
+++ b/widget/windows/WinMouseScrollHandler.h
@@ -1,5 +1,4 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=2 et sw=2 tw=80: */
 /* 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/. */
diff --git a/widget/windows/moz.build b/widget/windows/moz.build
index 4a449de95..baa9b8afc 100644
--- a/widget/windows/moz.build
+++ b/widget/windows/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.
diff --git a/widget/windows/nsNativeThemeWin.cpp b/widget/windows/nsNativeThemeWin.cpp
index e84a2b80c..0947019ca 100644
--- a/widget/windows/nsNativeThemeWin.cpp
+++ b/widget/windows/nsNativeThemeWin.cpp
@@ -1388,6 +1388,12 @@ GetThemeDpiScaleFactor(nsIFrame* aFrame)
   return 1.0;
 }
 
+static bool
+IsScrollbarWidthThin(nsIFrame* aFrame)
+{
+  return aFrame->StyleUserInterface()->mScrollbarWidth == StyleScrollbarWidth::Thin;
+}
+
 NS_IMETHODIMP
 nsNativeThemeWin::DrawWidgetBackground(nsRenderingContext* aContext,
                                        nsIFrame* aFrame,
@@ -2788,14 +2794,21 @@ nsNativeThemeWin::ClassicGetMinimumWidgetSize(nsIFrame* aFrame,
       break;
     case NS_THEME_SCROLLBARBUTTON_UP:
     case NS_THEME_SCROLLBARBUTTON_DOWN:
-      (*aResult).width = ::GetSystemMetrics(SM_CXVSCROLL);
-      (*aResult).height = ::GetSystemMetrics(SM_CYVSCROLL);
+      // Get scrollbar button metrics from the system, except in the case of
+      // thin scrollbars, where we leave them at 0 (collapsing them to invisible)
+      if (!IsScrollbarWidthThin(aFrame)) {
+        (*aResult).width = ::GetSystemMetrics(SM_CXVSCROLL);
+        (*aResult).height = ::GetSystemMetrics(SM_CYVSCROLL);
+      }
       *aIsOverridable = false;
       break;
     case NS_THEME_SCROLLBARBUTTON_LEFT:
     case NS_THEME_SCROLLBARBUTTON_RIGHT:
-      (*aResult).width = ::GetSystemMetrics(SM_CXHSCROLL);
-      (*aResult).height = ::GetSystemMetrics(SM_CYHSCROLL);
+      // See comment above.
+      if (!IsScrollbarWidthThin(aFrame)) {
+        (*aResult).width = ::GetSystemMetrics(SM_CXHSCROLL);
+        (*aResult).height = ::GetSystemMetrics(SM_CYHSCROLL);
+      }
       *aIsOverridable = false;
       break;
     case NS_THEME_SCROLLBAR_VERTICAL:
@@ -2871,8 +2884,14 @@ nsNativeThemeWin::ClassicGetMinimumWidgetSize(nsIFrame* aFrame,
       (*aResult).height = ::GetSystemMetrics(SM_CYVTHUMB);
       // Without theming, divide the thumb size by two in order to look more
       // native
-      if (!GetTheme(aWidgetType))
-        (*aResult).height >>= 1;
+      if (!GetTheme(aWidgetType)) {
+        (*aResult).height /= 2;
+      }
+      // If scrollbar-width is thin, divide the thickness by three to make
+      // it more compact.
+      if (IsScrollbarWidthThin(aFrame)) {
+        (*aResult).width /= 3;
+      }      
       *aIsOverridable = false;
       break;
     case NS_THEME_SCROLLBARTHUMB_HORIZONTAL:
@@ -2880,8 +2899,14 @@ nsNativeThemeWin::ClassicGetMinimumWidgetSize(nsIFrame* aFrame,
       (*aResult).height = ::GetSystemMetrics(SM_CYHSCROLL);
       // Without theming, divide the thumb size by two in order to look more
       // native
-      if (!GetTheme(aWidgetType))
-        (*aResult).width >>= 1;
+      if (!GetTheme(aWidgetType)) {
+        (*aResult).width /= 2;
+      }
+      // If scrollbar-width is thin, divide the thickness by three to make
+      // it more compact.
+      if (IsScrollbarWidthThin(aFrame)) {
+        (*aResult).height /= 3;
+      }      
       *aIsOverridable = false;
       break;
     case NS_THEME_SCROLLBAR_HORIZONTAL:
diff --git a/widget/windows/tests/moz.build b/widget/windows/tests/moz.build
index 28919c271..83ed8d9d9 100644
--- a/widget/windows/tests/moz.build
+++ b/widget/windows/tests/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.
diff --git a/widget/x11/moz.build b/widget/x11/moz.build
index 9b5dafb6d..2d5229fc8 100644
--- a/widget/x11/moz.build
+++ b/widget/x11/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.
diff --git a/widget/xremoteclient/moz.build b/widget/xremoteclient/moz.build
index 8d3f01c82..cac9f2d49 100644
--- a/widget/xremoteclient/moz.build
+++ b/widget/xremoteclient/moz.build
@@ -1,5 +1,4 @@
 # -*- 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/.