Issue #1667 - Part 2: Add MacOS 11.0 Big Sur widget compatibility

This involves refactoring the vibrancy and OpenGL/Pixel rendering changes contained
in the following Mozilla meta bugs: 1496823 and 1491445
Also add Big Sur to the features tests and update popup menu look and feel based
on Mozilla bug 1656301.

10 files changed, 286 insertions, 609 deletions

diff --git a/widget/cocoa/VibrancyManager.h b/widget/cocoa/VibrancyManager.h
index 7a7ea3af1..cae57a269 100644
--- a/widget/cocoa/VibrancyManager.h
+++ b/widget/cocoa/VibrancyManager.h
@@ -78,14 +78,6 @@ public:
   bool HasVibrantRegions() { return !mVibrantRegions.IsEmpty(); }
 
   /**
-   * Clear the vibrant areas that we know about.
-   * The clearing happens in the current NSGraphicsContext. If you call this
-   * from within an -[NSView drawRect:] implementation, the currrent
-   * NSGraphicsContext is already correctly set to the window drawing context.
-   */
-  void ClearVibrantAreas() const;
-
-  /**
    * Return the fill color that should be drawn on top of the cleared window
    * parts. Usually this would be drawn by -[NSVisualEffectView drawRect:].
    * The returned color is opaque if the system-wide "Reduce transparency"
@@ -106,10 +98,19 @@ public:
    */
   static bool SystemSupportsVibrancy();
 
-protected:
-  void ClearVibrantRegion(const LayoutDeviceIntRegion& aVibrantRegion) const;
-  NSView* CreateEffectView(VibrancyType aType);
+  /**
+   * Create an NSVisualEffectView for the specified vibrancy type. The return
+   * value is not autoreleased. We return an object of type NSView* because we
+   * compile with an SDK that does not contain a definition for
+   * NSVisualEffectView.
+   * @param aIsContainer Whether this NSView will have child views. This value
+   *                     affects hit testing: Container views will pass through
+   *                     hit testing requests to their children, and leaf views
+   *                     will be transparent to hit testing.
+   */
+  static NSView* CreateEffectView(VibrancyType aType, BOOL aIsContainer = NO);
 
+protected:
   const nsChildView& mCoordinateConverter;
   NSView* mContainerView;
   nsClassHashtable<nsUint32HashKey, ViewRegion> mVibrantRegions;
diff --git a/widget/cocoa/VibrancyManager.mm b/widget/cocoa/VibrancyManager.mm
index b6176de2b..93a774254 100644
--- a/widget/cocoa/VibrancyManager.mm
+++ b/widget/cocoa/VibrancyManager.mm
@@ -24,24 +24,6 @@ VibrancyManager::UpdateVibrantRegion(VibrancyType aType,
   });
 }
 
-void
-VibrancyManager::ClearVibrantAreas() const
-{
-  for (auto iter = mVibrantRegions.ConstIter(); !iter.Done(); iter.Next()) {
-    ClearVibrantRegion(iter.UserData()->Region());
-  }
-}
-
-void
-VibrancyManager::ClearVibrantRegion(const LayoutDeviceIntRegion& aVibrantRegion) const
-{
-  [[NSColor clearColor] set];
-
-  for (auto iter = aVibrantRegion.RectIter(); !iter.Done(); iter.Next()) {
-    NSRectFill(mCoordinateConverter.DevPixelsToCocoaPoints(iter.Get()));
-  }
-}
-
 @interface NSView(CurrentFillColor)
 - (NSColor*)_currentFillColor;
 @end
@@ -65,9 +47,8 @@ VibrancyManager::VibrancyFillColorForType(VibrancyType aType)
   NSView* view = mVibrantRegions.LookupOrAdd(uint32_t(aType))->GetAnyView();
 
   if (view && [view respondsToSelector:@selector(_currentFillColor)]) {
-    // -[NSVisualEffectView _currentFillColor] is the color that our view
-    // would draw during its drawRect implementation, if we hadn't
-    // disabled that.
+    // -[NSVisualEffectView _currentFillColor] is the color that the view
+    // draws in its drawRect implementation.
     return AdjustedColor([view _currentFillColor], aType);
   }
   return [NSColor whiteColor];
@@ -88,19 +69,6 @@ VibrancyManager::VibrancyFontSmoothingBackgroundColorForType(VibrancyType aType)
   return [NSColor clearColor];
 }
 
-static void
-DrawRectNothing(id self, SEL _cmd, NSRect aRect)
-{
-  // The super implementation would clear the background.
-  // That's fine for views that are placed below their content, but our
-  // setup is different: Our drawn content is drawn to mContainerView, which
-  // sits below this EffectView. So we must not clear the background here,
-  // because we'd erase that drawn content.
-  // Of course the regular content drawing still needs to clear the background
-  // behind vibrant areas. This is taken care of by having nsNativeThemeCocoa
-  // return true from NeedToClearBackgroundBehindWidget for vibrant widgets.
-}
-
 static NSView*
 HitTestNil(id self, SEL _cmd, NSPoint aPoint)
 {
@@ -116,21 +84,20 @@ AllowsVibrancyYes(id self, SEL _cmd)
 }
 
 static Class
-CreateEffectViewClass(BOOL aForegroundVibrancy)
+CreateEffectViewClass(BOOL aForegroundVibrancy, BOOL aIsContainer)
 {
-  // Create a class called EffectView that inherits from NSVisualEffectView
-  // and overrides the methods -[NSVisualEffectView drawRect:] and
-  // -[NSView hitTest:].
+  // Create a class that inherits from NSVisualEffectView and overrides the
+  // methods -[NSView hitTest:] and  -[NSVisualEffectView allowsVibrancy].
   Class NSVisualEffectViewClass = NSClassFromString(@"NSVisualEffectView");
   const char* className = aForegroundVibrancy
     ? "EffectViewWithForegroundVibrancy" : "EffectViewWithoutForegroundVibrancy";
   Class EffectViewClass = objc_allocateClassPair(NSVisualEffectViewClass, className, 0);
-  class_addMethod(EffectViewClass, @selector(drawRect:), (IMP)DrawRectNothing,
-                  "v@:{CGRect={CGPoint=dd}{CGSize=dd}}");
-  class_addMethod(EffectViewClass, @selector(hitTest:), (IMP)HitTestNil,
-                  "@@:{CGPoint=dd}");
+  if (!aIsContainer) {
+    class_addMethod(EffectViewClass, @selector(hitTest:), (IMP)HitTestNil,
+                    "@@:{CGPoint=dd}");
+  }
   if (aForegroundVibrancy) {
-    // Also override the -[NSView allowsVibrancy] method to return YES.
+    // Override the -[NSView allowsVibrancy] method to return YES.
     class_addMethod(EffectViewClass, @selector(allowsVibrancy), (IMP)AllowsVibrancyYes, "I@:");
   }
   return EffectViewClass;
@@ -217,13 +184,20 @@ enum {
 @end
 
 NSView*
-VibrancyManager::CreateEffectView(VibrancyType aType)
-{
-  static Class EffectViewClassWithoutForegroundVibrancy = CreateEffectViewClass(NO);
-  static Class EffectViewClassWithForegroundVibrancy = CreateEffectViewClass(YES);
-
-  Class EffectViewClass = HasVibrantForeground(aType)
-    ? EffectViewClassWithForegroundVibrancy : EffectViewClassWithoutForegroundVibrancy;
+VibrancyManager::CreateEffectView(VibrancyType aType, BOOL aIsContainer)
+{
+  static Class EffectViewWithoutForegroundVibrancy = CreateEffectViewClass(NO, NO);
+  static Class EffectViewWithForegroundVibrancy = CreateEffectViewClass(YES, NO);
+  static Class EffectViewContainer = CreateEffectViewClass(NO, YES);
+
+  // Pick the right NSVisualEffectView subclass for the desired vibrancy mode.
+  // For "container" views, never use foreground vibrancy, because returning
+  // YES from allowsVibrancy forces on foreground vibrancy for all descendant
+  // views which can have unintended effects.
+  Class EffectViewClass = aIsContainer
+                              ? EffectViewContainer
+                              : (HasVibrantForeground(aType) ? EffectViewWithForegroundVibrancy
+                                                             : EffectViewWithoutForegroundVibrancy);
   NSView* effectView = [[EffectViewClass alloc] initWithFrame:NSZeroRect];
   [effectView performSelector:@selector(setAppearance:)
                    withObject:AppearanceForVibrancyType(aType)];
diff --git a/widget/cocoa/mozView.h b/widget/cocoa/mozView.h
index 9e94e3ab4..bd054893b 100644
--- a/widget/cocoa/mozView.h
+++ b/widget/cocoa/mozView.h
@@ -34,11 +34,6 @@ class TextInputHandler;
   // return a context menu for this view
 - (NSMenu*)contextMenu;
 
-  // Allows callers to do a delayed invalidate (e.g., if an invalidate
-  // happens during drawing)
-- (void)setNeedsPendingDisplay;
-- (void)setNeedsPendingDisplayInRect:(NSRect)invalidRect;
-
   // called when our corresponding Gecko view goes away
 - (void)widgetDestroyed;
 
diff --git a/widget/cocoa/nsChildView.h b/widget/cocoa/nsChildView.h
index f6fb44633..2817c8d41 100644
--- a/widget/cocoa/nsChildView.h
+++ b/widget/cocoa/nsChildView.h
@@ -56,6 +56,8 @@ class WidgetRenderingContext;
 } // namespace widget
 } // namespace mozilla
 
+@class PixelHostingView;
+
 @interface NSEvent (Undocumented)
 
 // Return Cocoa event's corresponding Carbon event.  Not initialized (on
@@ -139,11 +141,6 @@ class WidgetRenderingContext;
   // when acceptsFirstMouse: is called, we store the event here (strong)
   NSEvent* mClickThroughMouseDownEvent;
 
-  // rects that were invalidated during a draw, so have pending drawing
-  NSMutableArray* mPendingDirtyRects;
-  BOOL mPendingFullDisplay;
-  BOOL mPendingDisplay;
-
   // WheelStart/Stop events should always come in pairs. This BOOL records the
   // last received event so that, when we receive one of the events, we make sure
   // to send its pair event first, in case we didn't yet for any reason.
@@ -185,8 +182,6 @@ class WidgetRenderingContext;
   float mCumulativeMagnification;
   float mCumulativeRotation;
 
-  BOOL mWaitingForPaint;
-
 #ifdef __LP64__
   // Support for fluid swipe tracking.
   BOOL* mCancelSwipeAnimation;
@@ -198,6 +193,15 @@ class WidgetRenderingContext;
   // The mask image that's used when painting into the titlebar using basic
   // CGContext painting (i.e. non-accelerated).
   CGImageRef mTopLeftCornerMask;
+
+  // Subviews of self, which act as container views for vibrancy views and
+  // non-draggable views.
+  NSView* mVibrancyViewsContainer;      // [STRONG]
+  NSView* mNonDraggableViewsContainer;  // [STRONG]
+
+  // The view that does our drawing. This is a subview of self so that it can
+  // be ordered on top of mVibrancyViewsContainer.
+  PixelHostingView* mPixelHostingView;
 }
 
 // class initialization
@@ -226,6 +230,10 @@ class WidgetRenderingContext;
 - (bool)preRender:(NSOpenGLContext *)aGLContext;
 - (void)postRender:(NSOpenGLContext *)aGLContext;
 
+- (NSView*)vibrancyViewsContainer;
+- (NSView*)nonDraggableViewsContainer;
+- (NSView*)pixelHostingView;
+
 - (BOOL)isCoveringTitlebar;
 
 - (void)viewWillStartLiveResize;
@@ -252,7 +260,6 @@ class WidgetRenderingContext;
 - (void)endGestureWithEvent:(NSEvent *)anEvent;
 
 - (void)scrollWheel:(NSEvent *)anEvent;
-- (void)handleAsyncScrollEvent:(CGEventRef)cgEvent ofType:(CGEventType)type;
 
 - (void)setUsingOMTCompositor:(BOOL)aUseOMTC;
 
@@ -507,8 +514,6 @@ public:
   void CleanupRemoteDrawing() override;
   bool InitCompositor(mozilla::layers::Compositor* aCompositor) override;
 
-  IAPZCTreeManager* APZCTM() { return mAPZC ; }
-
   NS_IMETHOD StartPluginIME(const mozilla::WidgetKeyboardEvent& aKeyboardEvent,
                             int32_t aPanelX, int32_t aPanelY,
                             nsString& aCommitted) override;
@@ -529,9 +534,6 @@ protected:
   void              ReportMoveEvent();
   void              ReportSizeEvent();
 
-  // override to create different kinds of child views. Autoreleases, so
-  // caller must retain.
-  virtual NSView*   CreateCocoaView(NSRect inFrame);
   void              TearDownView();
 
   virtual already_AddRefed<nsIWidget>
@@ -574,7 +576,7 @@ protected:
 
 protected:
 
-  NSView<mozView>*      mView;      // my parallel cocoa view (ChildView or NativeScrollbarView), [STRONG]
+  ChildView<mozView>* mView;  // my parallel cocoa view, [STRONG]
   RefPtr<mozilla::widget::TextInputHandler> mTextInputHandler;
   InputContext          mInputContext;
 
diff --git a/widget/cocoa/nsChildView.mm b/widget/cocoa/nsChildView.mm
index 1a257d899..95547a13e 100644
--- a/widget/cocoa/nsChildView.mm
+++ b/widget/cocoa/nsChildView.mm
@@ -146,7 +146,10 @@ bool gUserCancelledDrag = false;
 
 uint32_t nsChildView::sLastInputEventCount = 0;
 
-static uint32_t gNumberOfWidgetsNeedingEventThread = 0;
+// The view that will do our drawing or host our NSOpenGLContext or Core Animation layer.
+@interface PixelHostingView : NSView {
+}
+@end
 
 @interface ChildView(Private)
 
@@ -163,14 +166,9 @@ static uint32_t gNumberOfWidgetsNeedingEventThread = 0;
 
 - (BOOL)isRectObscuredBySubview:(NSRect)inRect;
 
-- (void)processPendingRedraws;
-
-- (void)drawRect:(NSRect)aRect inContext:(CGContextRef)aContext;
 - (LayoutDeviceIntRegion)nativeDirtyRegionWithBoundingRect:(NSRect)aRect;
-- (BOOL)isUsingMainThreadOpenGL;
 - (BOOL)isUsingOpenGL;
 - (void)drawUsingOpenGL;
-- (void)drawUsingOpenGLCallback;
 
 - (BOOL)hasRoundedBottomCorners;
 - (CGFloat)cornerRadius;
@@ -195,7 +193,6 @@ static uint32_t gNumberOfWidgetsNeedingEventThread = 0;
 
 - (LayoutDeviceIntPoint)convertWindowCoordinates:(NSPoint)aPoint;
 - (LayoutDeviceIntPoint)convertWindowCoordinatesRoundDown:(NSPoint)aPoint;
-- (IAPZCTreeManager*)apzctm;
 
 - (BOOL)inactiveWindowAcceptsMouseEvent:(NSEvent*)aEvent;
 - (void)updateWindowDraggableState;
@@ -204,26 +201,10 @@ static uint32_t gNumberOfWidgetsNeedingEventThread = 0;
 
 @end
 
-@interface EventThreadRunner : NSObject
-{
-  NSThread* mThread;
-}
-- (id)init;
-
-+ (void)start;
-+ (void)stop;
-
-@end
-
 @interface NSView(NSThemeFrameCornerRadius)
 - (float)roundedCornerRadius;
 @end
 
-@interface NSView(DraggableRegion)
-- (CGSRegionObj)_regionForOpaqueDescendants:(NSRect)aRect forMove:(BOOL)aForMove;
-- (CGSRegionObj)_regionForOpaqueDescendants:(NSRect)aRect forMove:(BOOL)aForMove forUnderTitlebar:(BOOL)aForUnderTitlebar;
-@end
-
 @interface NSWindow(NSWindowShouldZoomOnDoubleClick)
 + (BOOL)_shouldZoomOnDoubleClick; // present on 10.7 and above
 @end
@@ -380,13 +361,6 @@ nsChildView::~nsChildView()
 
   DestroyCompositor();
 
-  if (mAPZC && gfxPrefs::AsyncPanZoomSeparateEventThread()) {
-    gNumberOfWidgetsNeedingEventThread--;
-    if (gNumberOfWidgetsNeedingEventThread == 0) {
-      [EventThreadRunner stop];
-    }
-  }
-
   // An nsChildView object that was in use can be destroyed without Destroy()
   // ever being called on it.  So we also need to do a quick, safe cleanup
   // here (it's too late to just call Destroy(), which can cause crashes).
@@ -455,7 +429,8 @@ nsChildView::Create(nsIWidget* aParent,
   // that NS_NATIVE_WIDGET is the NSView.
   CGFloat scaleFactor = nsCocoaUtils::GetBackingScaleFactor(mParentView);
   NSRect r = nsCocoaUtils::DevPixelsToCocoaPoints(mBounds, scaleFactor);
-  mView = [(NSView<mozView>*)CreateCocoaView(r) retain];
+  mView = [[[[ChildView alloc] initWithFrame:r geckoChild:this] autorelease] retain];
+  
   if (!mView) {
     return NS_ERROR_FAILURE;
   }
@@ -488,17 +463,6 @@ nsChildView::Create(nsIWidget* aParent,
   NS_OBJC_END_TRY_ABORT_BLOCK_NSRESULT;
 }
 
-// Creates the appropriate child view. Override to create something other than
-// our |ChildView| object. Autoreleases, so caller must retain.
-NSView*
-nsChildView::CreateCocoaView(NSRect inFrame)
-{
-  NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NIL;
-
-  return [[[ChildView alloc] initWithFrame:inFrame geckoChild:this] autorelease];
-
-  NS_OBJC_END_TRY_ABORT_BLOCK_NIL;
-}
 
 void nsChildView::TearDownView()
 {
@@ -982,8 +946,9 @@ NS_IMETHODIMP nsChildView::Resize(double aWidth, double aHeight, bool aRepaint)
     [mView setFrame:DevPixelsToCocoaPoints(mBounds)];
   });
 
-  if (mVisible && aRepaint)
-    [mView setNeedsDisplay:YES];
+  if (mVisible && aRepaint) {
+    [[mView pixelHostingView] setNeedsDisplay:YES];
+  }
 
   NotifyRollupGeometryChange();
   ReportSizeEvent();
@@ -1021,8 +986,9 @@ NS_IMETHODIMP nsChildView::Resize(double aX, double aY,
     [mView setFrame:DevPixelsToCocoaPoints(mBounds)];
   });
 
-  if (mVisible && aRepaint)
-    [mView setNeedsDisplay:YES];
+  if (mVisible && aRepaint) {
+    [[mView pixelHostingView] setNeedsDisplay:YES];
+  }
 
   NotifyRollupGeometryChange();
   if (isMoving) {
@@ -1341,14 +1307,7 @@ NS_IMETHODIMP nsChildView::Invalidate(const LayoutDeviceIntRect& aRect)
   NS_ASSERTION(GetLayerManager()->GetBackendType() != LayersBackend::LAYERS_CLIENT,
                "Shouldn't need to invalidate with accelerated OMTC layers!");
 
-  if ([NSView focusView]) {
-    // if a view is focussed (i.e. being drawn), then postpone the invalidate so that we
-    // don't lose it.
-    [mView setNeedsPendingDisplayInRect:DevPixelsToCocoaPoints(aRect)];
-  }
-  else {
-    [mView setNeedsDisplayInRect:DevPixelsToCocoaPoints(aRect)];
-  }
+  [[mView pixelHostingView] setNeedsDisplayInRect:DevPixelsToCocoaPoints(aRect)];
 
   return NS_OK;
 
@@ -1920,13 +1879,6 @@ void
 nsChildView::ConfigureAPZCTreeManager()
 {
   nsBaseWidget::ConfigureAPZCTreeManager();
-
-  if (gfxPrefs::AsyncPanZoomSeparateEventThread()) {
-    if (gNumberOfWidgetsNeedingEventThread == 0) {
-      [EventThreadRunner start];
-    }
-    gNumberOfWidgetsNeedingEventThread++;
-  }
 }
 
 void
@@ -2557,14 +2509,6 @@ nsChildView::UpdateVibrancy(const nsTArray<ThemeGeometry>& aThemeGeometries)
   vm.UpdateVibrantRegion(VibrancyType::DARK, vibrantDarkRegion);
 }
 
-void
-nsChildView::ClearVibrantAreas()
-{
-  if (VibrancyManager::SystemSupportsVibrancy()) {
-    EnsureVibrancyManager().ClearVibrantAreas();
-  }
-}
-
 static VibrancyType
 ThemeGeometryTypeToVibrancyType(nsITheme::ThemeGeometryType aThemeGeometryType)
 {
@@ -2617,7 +2561,7 @@ nsChildView::EnsureVibrancyManager()
 {
   MOZ_ASSERT(mView, "Only call this once we have a view!");
   if (!mVibrancyManager) {
-    mVibrancyManager = MakeUnique<VibrancyManager>(*this, mView);
+    mVibrancyManager = MakeUnique<VibrancyManager>(*this, [mView vibrancyViewsContainer]);
   }
   return *mVibrancyManager;
 }
@@ -2787,9 +2731,10 @@ nsChildView::UpdateWindowDraggingRegion(const LayoutDeviceIntRegion& aRegion)
 
   // Suppress calls to setNeedsDisplay during NSView geometry changes.
   ManipulateViewWithoutNeedingDisplay(mView, ^() {
-    changed = mNonDraggableRegion.UpdateRegion(nonDraggable, *this, mView, ^() {
-      return [[NonDraggableView alloc] initWithFrame:NSZeroRect];
-    });
+    changed = mNonDraggableRegion.UpdateRegion(
+        nonDraggable, *this, [mView nonDraggableViewsContainer], ^() {
+          return [[NonDraggableView alloc] initWithFrame:NSZeroRect];
+        });
   });
 
   if (changed) {
@@ -3160,6 +3105,31 @@ private:
 
 #pragma mark -
 
+// ViewRegionContainerView is a view class for certain subviews of ChildView
+// which contain the NSViews created for ViewRegions (see ViewRegion.h).
+// It doesn't do anything interesting, it only acts as a container so that it's
+// easier for ChildView to control the z order of its children.
+@interface ViewRegionContainerView : NSView {
+}
+@end
+
+@implementation ViewRegionContainerView
+
+- (NSView*)hitTest:(NSPoint)aPoint {
+  return nil;  // Be transparent to mouse events.
+}
+
+- (BOOL)isFlipped {
+  return [[self superview] isFlipped];
+}
+
+- (BOOL)mouseDownCanMoveWindow {
+  return [[self superview] mouseDownCanMoveWindow];
+}
+
+@end
+;
+
 @implementation ChildView
 
 // globalDragPboard is non-null during native drag sessions that did not originate
@@ -3215,7 +3185,6 @@ NSEvent* gLastDragMouseDownEvent = nil;
 
   if ((self = [super initWithFrame:inFrame])) {
     mGeckoChild = inChild;
-    mPendingDisplay = NO;
     mBlockedLastMouseDown = NO;
     mExpectingWheelStop = NO;
 
@@ -3236,6 +3205,20 @@ NSEvent* gLastDragMouseDownEvent = nil;
     mCancelSwipeAnimation = nil;
 #endif
 
+    mNonDraggableViewsContainer = [[ViewRegionContainerView alloc] initWithFrame:[self bounds]];
+    mVibrancyViewsContainer = [[ViewRegionContainerView alloc] initWithFrame:[self bounds]];
+
+    [mNonDraggableViewsContainer setAutoresizingMask:NSViewWidthSizable | NSViewHeightSizable];
+    [mVibrancyViewsContainer setAutoresizingMask:NSViewWidthSizable | NSViewHeightSizable];
+
+    [self addSubview:mNonDraggableViewsContainer];
+    [self addSubview:mVibrancyViewsContainer];
+
+    mPixelHostingView = [[PixelHostingView alloc] initWithFrame:[self bounds]];
+    [mPixelHostingView setAutoresizingMask:NSViewWidthSizable | NSViewHeightSizable];
+
+    [self addSubview:mPixelHostingView];
+
     mTopLeftCornerMask = NULL;
   }
 
@@ -3250,10 +3233,9 @@ NSEvent* gLastDragMouseDownEvent = nil;
                                            selector:@selector(systemMetricsChanged)
                                                name:NSSystemColorsDidChangeNotification
                                              object:nil];
-  // TODO: replace the string with the constant once we build with the 10.7 SDK
   [[NSNotificationCenter defaultCenter] addObserver:self
                                            selector:@selector(scrollbarSystemMetricChanged)
-                                               name:@"NSPreferredScrollerStyleDidChangeNotification"
+                                               name:NSPreferredScrollerStyleDidChangeNotification
                                              object:nil];
   [[NSDistributedNotificationCenter defaultCenter] addObserver:self
                                                       selector:@selector(systemMetricsChanged)
@@ -3263,7 +3245,7 @@ NSEvent* gLastDragMouseDownEvent = nil;
   [[NSNotificationCenter defaultCenter] addObserver:self
                                            selector:@selector(_surfaceNeedsUpdate:)
                                                name:NSViewGlobalFrameDidChangeNotification
-                                             object:self];
+                                             object:mPixelHostingView];
 
   return self;
 
@@ -3348,12 +3330,23 @@ NSEvent* gLastDragMouseDownEvent = nil;
   NS_OBJC_END_TRY_ABORT_BLOCK;
 }
 
+- (NSView*)vibrancyViewsContainer {
+  return mVibrancyViewsContainer;
+}
+
+- (NSView*)nonDraggableViewsContainer {
+  return mNonDraggableViewsContainer;
+}
+
+- (NSView*)pixelHostingView {
+  return mPixelHostingView;
+}
+
 - (void)dealloc
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
 
   [mGLContext release];
-  [mPendingDirtyRects release];
   [mLastMouseDownEvent release];
   [mLastKeyDownEvent release];
   [mClickThroughMouseDownEvent release];
@@ -3362,6 +3355,12 @@ NSEvent* gLastDragMouseDownEvent = nil;
 
   [[NSNotificationCenter defaultCenter] removeObserver:self];
   [[NSDistributedNotificationCenter defaultCenter] removeObserver:self];
+  [mVibrancyViewsContainer removeFromSuperview];
+  [mVibrancyViewsContainer release];
+  [mNonDraggableViewsContainer removeFromSuperview];
+  [mNonDraggableViewsContainer release];
+  [mPixelHostingView removeFromSuperview];
+  [mPixelHostingView release];
 
   [super dealloc];
 
@@ -3408,82 +3407,6 @@ NSEvent* gLastDragMouseDownEvent = nil;
   }
 }
 
-- (void)setNeedsPendingDisplay
-{
-  NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
-
-  mPendingFullDisplay = YES;
-  if (!mPendingDisplay) {
-    [self performSelector:@selector(processPendingRedraws) withObject:nil afterDelay:0];
-    mPendingDisplay = YES;
-  }
-
-  NS_OBJC_END_TRY_ABORT_BLOCK;
-}
-
-- (void)setNeedsPendingDisplayInRect:(NSRect)invalidRect
-{
-  NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
-
-  if (!mPendingDirtyRects)
-    mPendingDirtyRects = [[NSMutableArray alloc] initWithCapacity:1];
-  [mPendingDirtyRects addObject:[NSValue valueWithRect:invalidRect]];
-  if (!mPendingDisplay) {
-    [self performSelector:@selector(processPendingRedraws) withObject:nil afterDelay:0];
-    mPendingDisplay = YES;
-  }
-
-  NS_OBJC_END_TRY_ABORT_BLOCK;
-}
-
-// Clears the queue of any pending invalides
-- (void)processPendingRedraws
-{
-  NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
-
-  if (mPendingFullDisplay) {
-    [self setNeedsDisplay:YES];
-  }
-  else if (mPendingDirtyRects) {
-    unsigned int count = [mPendingDirtyRects count];
-    for (unsigned int i = 0; i < count; ++i) {
-      [self setNeedsDisplayInRect:[[mPendingDirtyRects objectAtIndex:i] rectValue]];
-    }
-  }
-  mPendingFullDisplay = NO;
-  mPendingDisplay = NO;
-  [mPendingDirtyRects release];
-  mPendingDirtyRects = nil;
-
-  NS_OBJC_END_TRY_ABORT_BLOCK;
-}
-
-- (void)setNeedsDisplayInRect:(NSRect)aRect
-{
-  if (![self isUsingOpenGL]) {
-    [super setNeedsDisplayInRect:aRect];
-    return;
-  }
-
-  if ([[self window] isVisible] && [self isUsingMainThreadOpenGL]) {
-    // Draw without calling drawRect. This prevent us from
-    // needing to access the normal window buffer surface unnecessarily, so we
-    // waste less time synchronizing the two surfaces. (These synchronizations
-    // show up in a profiler as CGSDeviceLock / _CGSLockWindow /
-    // _CGSSynchronizeWindowBackingStore.) It also means that Cocoa doesn't
-    // have any potentially expensive invalid rect management for us.
-    if (!mWaitingForPaint) {
-      mWaitingForPaint = YES;
-      // Use NSRunLoopCommonModes instead of the default NSDefaultRunLoopMode
-      // so that the timer also fires while a native menu is open.
-      [self performSelector:@selector(drawUsingOpenGLCallback)
-                 withObject:nil
-                 afterDelay:0
-                    inModes:[NSArray arrayWithObject:NSRunLoopCommonModes]];
-    }
-  }
-}
-
 - (NSString*)description
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NIL;
@@ -3537,25 +3460,6 @@ NSEvent* gLastDragMouseDownEvent = nil;
   return YES;
 }
 
-- (void)scrollRect:(NSRect)aRect by:(NSSize)offset
-{
-  NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
-
-  // Update any pending dirty rects to reflect the new scroll position
-  if (mPendingDirtyRects) {
-    unsigned int count = [mPendingDirtyRects count];
-    for (unsigned int i = 0; i < count; ++i) {
-      NSRect oldRect = [[mPendingDirtyRects objectAtIndex:i] rectValue];
-      NSRect newRect = NSOffsetRect(oldRect, offset.width, offset.height);
-      [mPendingDirtyRects replaceObjectAtIndex:i
-                                    withObject:[NSValue valueWithRect:newRect]];
-    }
-  }
-  [super scrollRect:aRect by:offset];
-
-  NS_OBJC_END_TRY_ABORT_BLOCK;
-}
-
 - (BOOL)mouseDownCanMoveWindow
 {
   // Return YES so that parts of this view can be draggable. The non-draggable
@@ -3567,7 +3471,7 @@ NSEvent* gLastDragMouseDownEvent = nil;
 
 -(void)updateGLContext
 {
-  [mGLContext setView:self];
+  [mGLContext setView:mPixelHostingView];
   [mGLContext update];
 }
 
@@ -3580,11 +3484,6 @@ NSEvent* gLastDragMouseDownEvent = nil;
   }
 }
 
-- (BOOL)wantsBestResolutionOpenGLSurface
-{
-  return nsCocoaUtils::HiDPIEnabled() ? YES : NO;
-}
-
 - (void)viewDidChangeBackingProperties
 {
   [super viewDidChangeBackingProperties];
@@ -3646,7 +3545,7 @@ NSEvent* gLastDragMouseDownEvent = nil;
   LayoutDeviceIntRect boundingRect = mGeckoChild->CocoaPointsToDevPixels(aRect);
   const NSRect *rects;
   NSInteger count;
-  [self getRectsBeingDrawn:&rects count:&count];
+  [mPixelHostingView getRectsBeingDrawn:&rects count:&count];
 
   if (count > MAX_RECTS_IN_REGION) {
     return boundingRect;
@@ -3662,53 +3561,28 @@ NSEvent* gLastDragMouseDownEvent = nil;
 
 // The display system has told us that a portion of our view is dirty. Tell
 // gecko to paint it
-- (void)drawRect:(NSRect)aRect
+// This method is called from mPixelHostingView's drawRect handler.
+- (void)doDrawRect:(NSRect)aRect
 {
   CGContextRef cgContext = (CGContextRef)[[NSGraphicsContext currentContext] graphicsPort];
-  [self drawRect:aRect inContext:cgContext];
-
-  // If we're a transparent window and our contents have changed, we need
-  // to make sure the shadow is updated to the new contents.
-  if ([[self window] isKindOfClass:[BaseWindow class]]) {
-    [(BaseWindow*)[self window] deferredInvalidateShadow];
-  }
-}
 
-- (void)drawRect:(NSRect)aRect inContext:(CGContextRef)aContext
-{
   if (!mGeckoChild || !mGeckoChild->IsVisible())
     return;
 
-#ifdef DEBUG_UPDATE
-  LayoutDeviceIntRect geckoBounds = mGeckoChild->GetBounds();
-
-  fprintf (stderr, "---- Update[%p][%p] [%f %f %f %f] cgc: %p\n  gecko bounds: [%d %d %d %d]\n",
-           self, mGeckoChild,
-           aRect.origin.x, aRect.origin.y, aRect.size.width, aRect.size.height, aContext,
-           geckoBounds.x, geckoBounds.y, geckoBounds.width, geckoBounds.height);
-
-  CGAffineTransform xform = CGContextGetCTM(aContext);
-  fprintf (stderr, "  xform in: [%f %f %f %f %f %f]\n", xform.a, xform.b, xform.c, xform.d, xform.tx, xform.ty);
-#endif
-
   if ([self isUsingOpenGL]) {
-    // For Gecko-initiated repaints in OpenGL mode, drawUsingOpenGL is
-    // directly called from a delayed perform callback - without going through
-    // drawRect.
-    // Paints that come through here are triggered by something that Cocoa
-    // controls, for example by window resizing or window focus changes.
-
     // Since this view is usually declared as opaque, the window's pixel
     // buffer may now contain garbage which we need to prevent from reaching
     // the screen. The only place where garbage can show is in the window
     // corners and the vibrant regions of the window - the rest of the window
     // is covered by opaque content in our OpenGL surface.
     // So we need to clear the pixel buffer contents in these areas.
-    mGeckoChild->ClearVibrantAreas();
     [self clearCorners];
 
-    // Do GL composition and return.
-    [self drawUsingOpenGL];
+    // Force a sync OMTC composite into the OpenGL context and return.
+    LayoutDeviceIntRect geckoBounds = mGeckoChild->GetBounds();
+    LayoutDeviceIntRegion region(geckoBounds);
+
+    mGeckoChild->PaintWindow(region);
     return;
   }
 
@@ -3720,54 +3594,31 @@ NSEvent* gLastDragMouseDownEvent = nil;
   // multiple dev pixels. But Gecko expects its supplied context to be scaled
   // to device pixels, so we need to reverse the scaling.
   double scale = mGeckoChild->BackingScaleFactor();
-  CGContextSaveGState(aContext);
-  CGContextScaleCTM(aContext, 1.0 / scale, 1.0 / scale);
+  CGContextSaveGState(cgContext);
+  CGContextScaleCTM(cgContext, 1.0 / scale, 1.0 / scale);
 
   NSSize viewSize = [self bounds].size;
   gfx::IntSize backingSize = gfx::IntSize::Truncate(viewSize.width * scale, viewSize.height * scale);
   LayoutDeviceIntRegion region = [self nativeDirtyRegionWithBoundingRect:aRect];
 
-  bool painted = mGeckoChild->PaintWindowInContext(aContext, region, backingSize);
+  bool painted = mGeckoChild->PaintWindowInContext(cgContext, region, backingSize);
 
   // Undo the scale transform so that from now on the context is in
   // CocoaPoints again.
-  CGContextRestoreGState(aContext);
+  CGContextRestoreGState(cgContext);
 
-  if (!painted && [self isOpaque]) {
+  if (!painted && [mPixelHostingView isOpaque]) {
     // Gecko refused to draw, but we've claimed to be opaque, so we have to
     // draw something--fill with white.
-    CGContextSetRGBFillColor(aContext, 1, 1, 1, 1);
-    CGContextFillRect(aContext, NSRectToCGRect(aRect));
+    CGContextSetRGBFillColor(cgContext, 1, 1, 1, 1);
+    CGContextFillRect(cgContext, NSRectToCGRect(aRect));
   }
 
   if ([self isCoveringTitlebar]) {
     [self drawTitleString];
     [self drawTitlebarHighlight];
-    [self maskTopCornersInContext:aContext];
+    [self maskTopCornersInContext:cgContext];
   }
-
-#ifdef DEBUG_UPDATE
-  fprintf (stderr, "---- update done ----\n");
-
-#if 0
-  CGContextSetRGBStrokeColor (aContext,
-                            ((((unsigned long)self) & 0xff)) / 255.0,
-                            ((((unsigned long)self) & 0xff00) >> 8) / 255.0,
-                            ((((unsigned long)self) & 0xff0000) >> 16) / 255.0,
-                            0.5);
-#endif
-  CGContextSetRGBStrokeColor(aContext, 1, 0, 0, 0.8);
-  CGContextSetLineWidth(aContext, 4.0);
-  CGContextStrokeRect(aContext, NSRectToCGRect(aRect));
-#endif
-}
-
-- (BOOL)isUsingMainThreadOpenGL
-{
-  if (!mGeckoChild || ![self window])
-    return NO;
-
-  return mGeckoChild->GetLayerManager(nullptr)->GetBackendType() == mozilla::layers::LayersBackend::LAYERS_OPENGL;
 }
 
 - (BOOL)isUsingOpenGL
@@ -3775,33 +3626,9 @@ NSEvent* gLastDragMouseDownEvent = nil;
   if (!mGeckoChild || ![self window])
     return NO;
 
-  return mGLContext || mUsingOMTCompositor || [self isUsingMainThreadOpenGL];
-}
-
-- (void)drawUsingOpenGL
-{
-  PROFILER_LABEL("ChildView", "drawUsingOpenGL",
-    js::ProfileEntry::Category::GRAPHICS);
-
-  if (![self isUsingOpenGL] || !mGeckoChild->IsVisible())
-    return;
-
-  mWaitingForPaint = NO;
-
-  LayoutDeviceIntRect geckoBounds = mGeckoChild->GetBounds();
-  LayoutDeviceIntRegion region(geckoBounds);
-
-  mGeckoChild->PaintWindow(region);
+  return mGLContext || mUsingOMTCompositor;
 }
 
-// Called asynchronously after setNeedsDisplay in order to avoid entering the
-// normal drawing machinery.
-- (void)drawUsingOpenGLCallback
-{
-  if (mWaitingForPaint) {
-    [self drawUsingOpenGL];
-  }
-}
 
 - (BOOL)hasRoundedBottomCorners
 {
@@ -4803,12 +4630,6 @@ GetIntegerDeltaForEvent(NSEvent* aEvent)
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
 
-  if (gfxPrefs::AsyncPanZoomSeparateEventThread() && [self apzctm]) {
-    // Disable main-thread scrolling completely when using APZ with the
-    // separate event thread. This is bug 1013412.
-    return;
-  }
-
   nsAutoRetainCocoaObject kungFuDeathGrip(self);
 
   ChildViewMouseTracker::MouseScrolled(theEvent);
@@ -4928,105 +4749,6 @@ GetIntegerDeltaForEvent(NSEvent* aEvent)
   NS_OBJC_END_TRY_ABORT_BLOCK;
 }
 
-- (void)handleAsyncScrollEvent:(CGEventRef)cgEvent ofType:(CGEventType)type
-{
-  IAPZCTreeManager* apzctm = [self apzctm];
-  if (!apzctm) {
-    return;
-  }
-
-  CGPoint loc = CGEventGetLocation(cgEvent);
-  loc.y = nsCocoaUtils::FlippedScreenY(loc.y);
-  NSPoint locationInWindow =
-    nsCocoaUtils::ConvertPointFromScreen([self window], NSPointFromCGPoint(loc));
-  ScreenIntPoint location = ViewAs<ScreenPixel>(
-    [self convertWindowCoordinates:locationInWindow],
-    PixelCastJustification::LayoutDeviceIsScreenForUntransformedEvent);
-
-  static NSTimeInterval sStartTime = [NSDate timeIntervalSinceReferenceDate];
-  static TimeStamp sStartTimeStamp = TimeStamp::Now();
-
-  if (type == kCGEventScrollWheel) {
-    NSEvent* event = [NSEvent eventWithCGEvent:cgEvent];
-    NSEventPhase phase = nsCocoaUtils::EventPhase(event);
-    NSEventPhase momentumPhase = nsCocoaUtils::EventMomentumPhase(event);
-    CGFloat pixelDeltaX = 0, pixelDeltaY = 0;
-    nsCocoaUtils::GetScrollingDeltas(event, &pixelDeltaX, &pixelDeltaY);
-    uint32_t eventTime = ([event timestamp] - sStartTime) * 1000;
-    TimeStamp eventTimeStamp = sStartTimeStamp +
-      TimeDuration::FromSeconds([event timestamp] - sStartTime);
-    NSPoint locationInWindowMoved = NSMakePoint(
-      locationInWindow.x + pixelDeltaX,
-      locationInWindow.y - pixelDeltaY);
-    ScreenIntPoint locationMoved = ViewAs<ScreenPixel>(
-      [self convertWindowCoordinates:locationInWindowMoved],
-      PixelCastJustification::LayoutDeviceIsScreenForUntransformedEvent);
-    ScreenPoint delta = ScreenPoint(locationMoved - location);
-    ScrollableLayerGuid guid;
-
-    // MayBegin and Cancelled are dispatched when the fingers start or stop
-    // touching the touchpad before any scrolling has occurred. These events
-    // can be used to control scrollbar visibility or interrupt scroll
-    // animations. They are only dispatched on 10.8 or later, and only by
-    // relatively modern devices.
-    if (phase == NSEventPhaseMayBegin) {
-      PanGestureInput panInput(PanGestureInput::PANGESTURE_MAYSTART, eventTime,
-                               eventTimeStamp, location, ScreenPoint(0, 0), 0);
-      apzctm->ReceiveInputEvent(panInput, &guid, nullptr);
-      return;
-    }
-    if (phase == NSEventPhaseCancelled) {
-      PanGestureInput panInput(PanGestureInput::PANGESTURE_CANCELLED, eventTime,
-                               eventTimeStamp, location, ScreenPoint(0, 0), 0);
-      apzctm->ReceiveInputEvent(panInput, &guid, nullptr);
-      return;
-    }
-
-    // Legacy scroll events are dispatched by devices that do not have a
-    // concept of a scroll gesture, for example by USB mice with
-    // traditional mouse wheels.
-    // For these kinds of scrolls, we want to surround every single scroll
-    // event with a PANGESTURE_START and a PANGESTURE_END event. The APZC
-    // needs to know that the real scroll gesture can end abruptly after any
-    // one of these events.
-    bool isLegacyScroll = (phase == NSEventPhaseNone &&
-      momentumPhase == NSEventPhaseNone && delta != ScreenPoint(0, 0));
-
-    if (phase == NSEventPhaseBegan || isLegacyScroll) {
-      PanGestureInput panInput(PanGestureInput::PANGESTURE_START, eventTime,
-                               eventTimeStamp, location, ScreenPoint(0, 0), 0);
-      apzctm->ReceiveInputEvent(panInput, &guid, nullptr);
-    }
-    if (momentumPhase == NSEventPhaseNone && delta != ScreenPoint(0, 0)) {
-      PanGestureInput panInput(PanGestureInput::PANGESTURE_PAN, eventTime,
-                               eventTimeStamp, location, delta, 0);
-      apzctm->ReceiveInputEvent(panInput, &guid, nullptr);
-    }
-    if (phase == NSEventPhaseEnded || isLegacyScroll) {
-      PanGestureInput panInput(PanGestureInput::PANGESTURE_END, eventTime,
-                               eventTimeStamp, location, ScreenPoint(0, 0), 0);
-      apzctm->ReceiveInputEvent(panInput, &guid, nullptr);
-    }
-
-    // Any device that can dispatch momentum events supports all three momentum phases.
-    if (momentumPhase == NSEventPhaseBegan) {
-      PanGestureInput panInput(PanGestureInput::PANGESTURE_MOMENTUMSTART, eventTime,
-                               eventTimeStamp, location, ScreenPoint(0, 0), 0);
-      apzctm->ReceiveInputEvent(panInput, &guid, nullptr);
-    }
-    if (momentumPhase == NSEventPhaseChanged && delta != ScreenPoint(0, 0)) {
-      PanGestureInput panInput(PanGestureInput::PANGESTURE_MOMENTUMPAN, eventTime,
-                               eventTimeStamp, location, delta, 0);
-      apzctm->ReceiveInputEvent(panInput, &guid, nullptr);
-    }
-    if (momentumPhase == NSEventPhaseEnded) {
-      PanGestureInput panInput(PanGestureInput::PANGESTURE_MOMENTUMEND, eventTime,
-                               eventTimeStamp, location, ScreenPoint(0, 0), 0);
-      apzctm->ReceiveInputEvent(panInput, &guid, nullptr);
-    }
-  }
-}
-
 -(NSMenu*)menuForEvent:(NSEvent*)theEvent
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NIL;
@@ -5571,11 +5293,6 @@ GetIntegerDeltaForEvent(NSEvent* aEvent)
   return mGeckoChild->CocoaPointsToDevPixelsRoundDown(localPoint);
 }
 
-- (IAPZCTreeManager*)apzctm
-{
-  return mGeckoChild ? mGeckoChild->APZCTM() : nullptr;
-}
-
 // This is a utility function used by NSView drag event methods
 // to send events. It contains all of the logic needed for Gecko
 // dragging to work. Returns the appropriate cocoa drag operation code.
@@ -6209,6 +5926,26 @@ nsChildView::GetSelectionAsPlaintext(nsAString& aResult)
 
 @end
 
+@implementation PixelHostingView
+
+- (BOOL)isFlipped {
+  return YES;
+}
+
+- (NSView*)hitTest:(NSPoint)aPoint {
+  return nil;
+}
+
+- (void)drawRect:(NSRect)aRect {
+  [(ChildView*)[self superview] doDrawRect:aRect];
+}
+
+- (BOOL)wantsBestResolutionOpenGLSurface {
+  return nsCocoaUtils::HiDPIEnabled() ? YES : NO;
+}
+
+@end
+
 #pragma mark -
 
 void
@@ -6377,106 +6114,6 @@ ChildViewMouseTracker::WindowAcceptsEvent(NSWindow* aWindow, NSEvent* aEvent,
 
 #pragma mark -
 
-@interface EventThreadRunner(Private)
-- (void)runEventThread;
-- (void)shutdownAndReleaseCalledOnEventThread;
-- (void)shutdownAndReleaseCalledOnAnyThread;
-- (void)handleEvent:(CGEventRef)cgEvent type:(CGEventType)type;
-@end
-
-static EventThreadRunner* sEventThreadRunner = nil;
-
-@implementation EventThreadRunner
-
-+ (void)start
-{
-  sEventThreadRunner = [[EventThreadRunner alloc] init];
-}
-
-+ (void)stop
-{
-  if (sEventThreadRunner) {
-    [sEventThreadRunner shutdownAndReleaseCalledOnAnyThread];
-    sEventThreadRunner = nil;
-  }
-}
-
-- (id)init
-{
-  if ((self = [super init])) {
-    mThread = nil;
-    [NSThread detachNewThreadSelector:@selector(runEventThread)
-                             toTarget:self
-                           withObject:nil];
-  }
-  return self;
-}
-
-static CGEventRef
-HandleEvent(CGEventTapProxy aProxy, CGEventType aType,
-            CGEventRef aEvent, void* aClosure)
-{
-  [(EventThreadRunner*)aClosure handleEvent:aEvent type:aType];
-  return aEvent;
-}
-
-- (void)runEventThread
-{
-  char aLocal;
-  profiler_register_thread("APZC Event Thread", &aLocal);
-  PR_SetCurrentThreadName("APZC Event Thread");
-
-  mThread = [NSThread currentThread];
-  ProcessSerialNumber currentProcess;
-  GetCurrentProcess(&currentProcess);
-  CFMachPortRef eventPort =
-    CGEventTapCreateForPSN(&currentProcess,
-                           kCGHeadInsertEventTap,
-                           kCGEventTapOptionListenOnly,
-                           CGEventMaskBit(kCGEventScrollWheel),
-                           HandleEvent,
-                           self);
-  CFRunLoopSourceRef eventPortSource =
-    CFMachPortCreateRunLoopSource(kCFAllocatorSystemDefault, eventPort, 0);
-  CFRunLoopAddSource(CFRunLoopGetCurrent(), eventPortSource, kCFRunLoopCommonModes);
-  CFRunLoopRun();
-  CFRunLoopRemoveSource(CFRunLoopGetCurrent(), eventPortSource, kCFRunLoopCommonModes);
-  CFRelease(eventPortSource);
-  CFRelease(eventPort);
-  [self release];
-}
-
-- (void)shutdownAndReleaseCalledOnEventThread
-{
-  CFRunLoopStop(CFRunLoopGetCurrent());
-}
-
-- (void)shutdownAndReleaseCalledOnAnyThread
-{
-  [self performSelector:@selector(shutdownAndReleaseCalledOnEventThread) onThread:mThread withObject:nil waitUntilDone:NO];
-}
-
-static const CGEventField kCGWindowNumberField = (const CGEventField) 51;
-
-// Called on scroll thread
-- (void)handleEvent:(CGEventRef)cgEvent type:(CGEventType)type
-{
-  if (type != kCGEventScrollWheel) {
-    return;
-  }
-
-  int windowNumber = CGEventGetIntegerValueField(cgEvent, kCGWindowNumberField);
-  NSWindow* window = [NSApp windowWithWindowNumber:windowNumber];
-  if (!window || ![window isKindOfClass:[BaseWindow class]]) {
-    return;
-  }
-
-  ChildView* childView = [(BaseWindow*)window mainChildView];
-  [childView handleAsyncScrollEvent:cgEvent ofType:type];
-}
-
-@end
-
 @interface NSView (MethodSwizzling)
 - (BOOL)nsChildView_NSView_mouseDownCanMoveWindow;
 @end
diff --git a/widget/cocoa/nsCocoaFeatures.h b/widget/cocoa/nsCocoaFeatures.h
index 984dae80e..7ebbe759f 100644
--- a/widget/cocoa/nsCocoaFeatures.h
+++ b/widget/cocoa/nsCocoaFeatures.h
@@ -24,6 +24,7 @@ public:
   static bool OnHighSierraOrLater();
   static bool OnMojaveOrLater();
   static bool OnCatalinaOrLater();
+  static bool OnBigSurOrLater();
 
   static bool IsAtLeastVersion(int32_t aMajor, int32_t aMinor, int32_t aBugFix=0);
 
diff --git a/widget/cocoa/nsCocoaFeatures.mm b/widget/cocoa/nsCocoaFeatures.mm
index 065260837..0b22c51bd 100644
--- a/widget/cocoa/nsCocoaFeatures.mm
+++ b/widget/cocoa/nsCocoaFeatures.mm
@@ -22,6 +22,8 @@
 #define MAC_OS_X_VERSION_10_13_HEX 0x000010D0
 #define MAC_OS_X_VERSION_10_14_HEX 0x000010E0
 #define MAC_OS_X_VERSION_10_15_HEX 0x000010F0
+#define MAC_OS_X_VERSION_10_16_HEX 0x000A1000
+#define MAC_OS_X_VERSION_11_0_HEX  0x000B0000
 
 #include "nsCocoaFeatures.h"
 #include "nsCocoaUtils.h"
@@ -189,6 +191,14 @@ nsCocoaFeatures::OnCatalinaOrLater()
 }
 
 /* static */ bool
+nsCocoaFeatures::OnBigSurOrLater() {
+  // Account for the version being 10.16 (which occurs when the
+  // application is linked with an older SDK) or 11.0 on Big Sur.
+  return ((OSXVersion() >= MAC_OS_X_VERSION_10_16_HEX) ||
+          (OSXVersion() >= MAC_OS_X_VERSION_11_0_HEX));
+}
+
+/* static */ bool
 nsCocoaFeatures::IsAtLeastVersion(int32_t aMajor, int32_t aMinor, int32_t aBugFix)
 {
     return OSXVersion() >= GetVersion(aMajor, aMinor, aBugFix);
diff --git a/widget/cocoa/nsCocoaWindow.h b/widget/cocoa/nsCocoaWindow.h
index 6338f474d..1913696b8 100644
--- a/widget/cocoa/nsCocoaWindow.h
+++ b/widget/cocoa/nsCocoaWindow.h
@@ -359,7 +359,8 @@ protected:
   nsresult             CreateNativeWindow(const NSRect &aRect,
                                           nsBorderStyle aBorderStyle,
                                           bool aRectIsFrameRect);
-  nsresult             CreatePopupContentView(const LayoutDeviceIntRect &aRect);
+  nsresult             CreatePopupContentView(const LayoutDeviceIntRect &aRect,
+                                              nsWidgetInitData* aInitData);
   void                 DestroyNativeWindow();
   void                 AdjustWindowShadow();
   void                 SetWindowBackgroundBlur();
@@ -416,6 +417,8 @@ protected:
   bool                 mInReportMoveEvent; // true if in a call to ReportMoveEvent().
   bool                 mInResize; // true if in a call to DoResize().
 
+  bool                 mAlwaysOnTop;
+
   int32_t              mNumModalDescendents;
   InputContext         mInputContext;
 };
diff --git a/widget/cocoa/nsCocoaWindow.mm b/widget/cocoa/nsCocoaWindow.mm
index b6d94ea94..b141e80b0 100644
--- a/widget/cocoa/nsCocoaWindow.mm
+++ b/widget/cocoa/nsCocoaWindow.mm
@@ -35,6 +35,7 @@
 #include "nsIWidgetListener.h"
 #include "nsIPresShell.h"
 #include "nsScreenCocoa.h"
+#include "VibrancyManager.h"
 
 #include "gfxPlatform.h"
 #include "qcms.h"
@@ -128,6 +129,7 @@ nsCocoaWindow::nsCocoaWindow()
 , mIsAnimationSuppressed(false)
 , mInReportMoveEvent(false)
 , mInResize(false)
+, mAlwaysOnTop(false)
 , mNumModalDescendents(0)
 {
   if ([NSWindow respondsToSelector:@selector(setAllowsAutomaticWindowTabbing:)]) {
@@ -302,12 +304,14 @@ nsCocoaWindow::Create(nsIWidget* aParent,
   if (mWindowType == eWindowType_popup) {
     if (aInitData->mMouseTransparent) {
       [mWindow setIgnoresMouseEvents:YES];
+    } else {
+      [mWindow setIgnoresMouseEvents:NO];
     }
     // now we can convert newBounds to device pixels for the window we created,
     // as the child view expects a rect expressed in the dev pix of its parent
     LayoutDeviceIntRect devRect =
       RoundedToInt(newBounds * GetDesktopToDeviceScale());
-    return CreatePopupContentView(devRect);
+    return CreatePopupContentView(devRect, aInitData);
   }
 
   mIsAnimationSuppressed = aInitData->mIsAnimationSuppressed;
@@ -456,6 +460,11 @@ nsresult nsCocoaWindow::CreateNativeWindow(const NSRect &aRect,
   mWindow = [[windowClass alloc] initWithContentRect:contentRect styleMask:features 
                                  backing:NSBackingStoreBuffered defer:YES];
 
+  // Make sure that window titles don't leak to disk in private browsing mode
+  // due to macOS' resume feature.
+  [mWindow setRestorable:NO];
+  [mWindow disableSnapshotRestoration];
+
   // setup our notification delegate. Note that setDelegate: does NOT retain.
   mDelegate = [[WindowDelegate alloc] initWithGeckoWindow:this];
   [mWindow setDelegate:mDelegate];
@@ -474,7 +483,6 @@ nsresult nsCocoaWindow::CreateNativeWindow(const NSRect &aRect,
 
   if (mWindowType == eWindowType_popup) {
     SetPopupWindowLevel();
-    [mWindow setHasShadow:YES];
     [mWindow setBackgroundColor:[NSColor clearColor]];
     [mWindow setOpaque:NO];
   } else {
@@ -483,6 +491,13 @@ nsresult nsCocoaWindow::CreateNativeWindow(const NSRect &aRect,
     [mWindow setOpaque:YES];
   }
 
+  NSWindowCollectionBehavior newBehavior = [mWindow collectionBehavior];
+  if (mAlwaysOnTop) {
+    [mWindow setLevel:NSFloatingWindowLevel];
+    newBehavior |= NSWindowCollectionBehaviorCanJoinAllSpaces;
+  }
+  [mWindow setCollectionBehavior:newBehavior];
+
   [mWindow setContentMinSize:NSMakeSize(60, 60)];
   [mWindow disableCursorRects];
 
@@ -499,7 +514,8 @@ nsresult nsCocoaWindow::CreateNativeWindow(const NSRect &aRect,
 }
 
 NS_IMETHODIMP
-nsCocoaWindow::CreatePopupContentView(const LayoutDeviceIntRect &aRect)
+nsCocoaWindow::CreatePopupContentView(const LayoutDeviceIntRect &aRect,
+	                                  nsWidgetInitData* aInitData)
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NSRESULT;
 
@@ -512,13 +528,16 @@ nsCocoaWindow::CreatePopupContentView(const LayoutDeviceIntRect &aRect)
 
   nsIWidget* thisAsWidget = static_cast<nsIWidget*>(this);
   nsresult rv = mPopupContentView->Create(thisAsWidget, nullptr, aRect,
-                                          nullptr);
+                                          aInitData);
   if (NS_WARN_IF(NS_FAILED(rv))) {
     return rv;
   }
 
-  ChildView* newContentView = (ChildView*)mPopupContentView->GetNativeData(NS_NATIVE_WIDGET);
-  [mWindow setContentView:newContentView];
+  NSView* contentView = [mWindow contentView];
+  ChildView* childView = (ChildView*)mPopupContentView->GetNativeData(NS_NATIVE_WIDGET);
+  [childView setFrame:NSZeroRect];
+  [childView setAutoresizingMask:NSViewWidthSizable | NSViewHeightSizable];
+  [contentView addSubview:childView];
 
   return NS_OK;
 
@@ -757,6 +776,13 @@ NS_IMETHODIMP nsCocoaWindow::Show(bool bState)
     (NSWindow*)parentWidget->GetNativeData(NS_NATIVE_WINDOW) : nil;
 
   if (bState && !mBounds.IsEmpty()) {
+    // Don't try to show a popup when the parent isn't visible or is minimized.
+    if (mWindowType == eWindowType_popup && nativeParentWindow) {
+      if (![nativeParentWindow isVisible] || [nativeParentWindow isMiniaturized]) {
+        return NS_ERROR_FAILURE;
+      }
+    }
+
     if (mPopupContentView) {
       // Ensure our content view is visible. We never need to hide it.
       mPopupContentView->Show(true);
@@ -2790,12 +2816,6 @@ static NSMutableSet *gSwizzledFrameViewClasses = nil;
  - (void)_addKnownSubview:(NSView*)aView positioned:(NSWindowOrderingMode)place relativeTo:(NSView*)otherView;
 @end
 
-// Available on 10.10
-@interface NSWindow(PrivateCornerMaskMethod)
- - (id)_cornerMask;
- - (void)_cornerMaskChanged;
-@end
-
 #if !defined(MAC_OS_X_VERSION_10_10) || \
     MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_10
 
@@ -2816,6 +2836,10 @@ static NSMutableSet *gSwizzledFrameViewClasses = nil;
 
 #endif
 
+@interface NSView(NSVisualEffectViewSetMaskImage)
+- (void)setMaskImage:(NSImage*)image;
+@end
+
 @interface BaseWindow(Private)
 - (void)removeTrackingArea;
 - (void)cursorUpdated:(NSEvent*)aEvent;
@@ -2825,25 +2849,6 @@ static NSMutableSet *gSwizzledFrameViewClasses = nil;
 
 @implementation BaseWindow
 
-- (id)_cornerMask
-{
-  if (!mUseMenuStyle) {
-    return [super _cornerMask];
-  }
-
-  CGFloat radius = 4.0f;
-  NSEdgeInsets insets = { 5, 5, 5, 5 };
-  NSSize maskSize = { 12, 12 };
-  NSImage* maskImage = [NSImage imageWithSize:maskSize flipped:YES drawingHandler:^BOOL(NSRect dstRect) {
-    NSBezierPath *path = [NSBezierPath bezierPathWithRoundedRect:dstRect xRadius:radius yRadius:radius];
-    [[NSColor colorWithDeviceWhite:1.0 alpha:1.0] set];
-    [path fill];
-    return YES;
-  }];
-  [maskImage setCapInsets:insets];
-  return maskImage;
-}
-
 // The frame of a window is implemented using undocumented NSView subclasses.
 // We offset the window buttons by overriding the methods _closeButtonOrigin
 // and _fullScreenButtonOrigin on these frame view classes. The class which is
@@ -2916,14 +2921,54 @@ static NSMutableSet *gSwizzledFrameViewClasses = nil;
   return self;
 }
 
+// Returns an autoreleased NSImage.
+static NSImage*
+GetMenuMaskImage()
+{
+  CGFloat radius = 4.0f;
+  NSEdgeInsets insets = { 5, 5, 5, 5 };
+  NSSize maskSize = { 12, 12 };
+  NSImage* maskImage = [NSImage imageWithSize:maskSize flipped:YES drawingHandler:^BOOL(NSRect dstRect) {
+    NSBezierPath *path = [NSBezierPath bezierPathWithRoundedRect:dstRect xRadius:radius yRadius:radius];
+    [[NSColor colorWithDeviceWhite:1.0 alpha:1.0] set];
+    [path fill];
+    return YES;
+  }];
+  [maskImage setCapInsets:insets];
+  return maskImage;
+}
+
+- (void)swapOutChildViewWrapper:(NSView*)aNewWrapper
+{
+  [aNewWrapper setFrame:[[self contentView] frame]];
+  NSView* childView = [[self mainChildView] retain];
+  [childView removeFromSuperview];
+  [aNewWrapper addSubview:childView];
+  [childView release];
+  [super setContentView:aNewWrapper];
+}
+
 - (void)setUseMenuStyle:(BOOL)aValue
 {
-  if (aValue != mUseMenuStyle) {
-    mUseMenuStyle = aValue;
-    if ([self respondsToSelector:@selector(_cornerMaskChanged)]) {
-      [self _cornerMaskChanged];
+  if (!VibrancyManager::SystemSupportsVibrancy()) {
+    return;
+  }
+
+  if (aValue && !mUseMenuStyle) {
+    // Turn on rounded corner masking.
+    NSView* effectView = VibrancyManager::CreateEffectView(VibrancyType::MENU, YES);
+    if ([effectView respondsToSelector:@selector(setMaskImage:)]) {
+      [effectView setMaskImage:GetMenuMaskImage()];
     }
+    [self swapOutChildViewWrapper:effectView];
+    [effectView release];
+  } else if (mUseMenuStyle && !aValue) {
+    // Turn off rounded corner masking.
+    NSView* wrapper = [[NSView alloc] initWithFrame:NSZeroRect];
+    [self swapOutChildViewWrapper:wrapper];
+    [wrapper release];
   }
+  mUseMenuStyle = aValue;
 }
 
 - (void)setBeingShown:(BOOL)aValue
@@ -3081,10 +3126,6 @@ static const NSString* kStateCollectionBehavior = @"collectionBehavior";
 - (ChildView*)mainChildView
 {
   NSView *contentView = [self contentView];
-  // A PopupWindow's contentView is a ChildView object.
-  if ([contentView isKindOfClass:[ChildView class]]) {
-    return (ChildView*)contentView;
-  }
   NSView* lastView = [[contentView subviews] lastObject];
   if ([lastView isKindOfClass:[ChildView class]]) {
     return (ChildView*)lastView;
diff --git a/widget/cocoa/nsNativeThemeCocoa.mm b/widget/cocoa/nsNativeThemeCocoa.mm
index fc4f7f2e9..f93e40f7b 100644
--- a/widget/cocoa/nsNativeThemeCocoa.mm
+++ b/widget/cocoa/nsNativeThemeCocoa.mm
@@ -443,8 +443,8 @@ static ChildView* ChildViewForFrame(nsIFrame* aFrame)
   if (!widget)
     return nil;
 
-  NSView* view = (NSView*)widget->GetNativeData(NS_NATIVE_WIDGET);
-  return [view isKindOfClass:[ChildView class]] ? (ChildView*)view : nil;
+  NSWindow* window = (NSWindow*)widget->GetNativeData(NS_NATIVE_WINDOW);
+  return [window isKindOfClass:[BaseWindow class]] ? [(BaseWindow*)window mainChildView]  : nil;
 }
 
 static NSWindow* NativeWindowForFrame(nsIFrame* aFrame,
@@ -2437,17 +2437,30 @@ nsNativeThemeCocoa::DrawWidgetBackground(nsRenderingContext* aContext,
       break;
 
     case NS_THEME_MENUSEPARATOR: {
-      ThemeMenuState menuState;
-      if (IsDisabled(aFrame, eventState)) {
-        menuState = kThemeMenuDisabled;
+      // Workaround for visual artifacts issues with
+      // HIThemeDrawMenuSeparator on macOS Big Sur.
+      if (nsCocoaFeatures::OnBigSurOrLater()) {
+        CGRect separatorRect = macRect;
+        separatorRect.size.height = 1;
+        separatorRect.size.width -= 42;
+        separatorRect.origin.x += 21;
+        // Use a gray color similar to the native separator
+        CGContextSetRGBFillColor(cgContext, 0.816, 0.816, 0.816, 1.0);
+        CGContextFillRect(cgContext, separatorRect);
       }
-      else {
-        menuState = CheckBooleanAttr(aFrame, nsGkAtoms::menuactive) ?
-                    kThemeMenuSelected : kThemeMenuActive;
+      else
+      {
+        ThemeMenuState menuState;
+        if (IsDisabled(aFrame, eventState)) {
+           menuState = kThemeMenuDisabled;
+        }
+        else {
+          menuState = CheckBooleanAttr(aFrame, nsGkAtoms::menuactive) ?
+                      kThemeMenuSelected : kThemeMenuActive;
+        }
+        HIThemeMenuItemDrawInfo midi = { 0, kThemeMenuItemPlain, menuState };
+        HIThemeDrawMenuSeparator(&macRect, &macRect, &midi, cgContext, HITHEME_ORIENTATION);
       }
-
-      HIThemeMenuItemDrawInfo midi = { 0, kThemeMenuItemPlain, menuState };
-      HIThemeDrawMenuSeparator(&macRect, &macRect, &midi, cgContext, HITHEME_ORIENTATION);
     }
       break;