--- a/widget/cocoa/nsCocoaWindow.h
+++ b/widget/cocoa/nsCocoaWindow.h
@@ -128,23 +128,26 @@ typedef struct _nsCocoaWindowList {
 + (Class)frameViewClassForStyleMask:(NSUInteger)styleMask;
 
 @end
 
 @interface PopupWindow : BaseWindow
 {
 @private
   BOOL mIsContextMenu;
+  BOOL mIsArrowPanel;
+  NSPoint mArrowPanelArrowTip;
 }
 
 - (id)initWithContentRect:(NSRect)contentRect styleMask:(NSUInteger)styleMask
       backing:(NSBackingStoreType)bufferingType defer:(BOOL)deferCreation;
 - (BOOL)isContextMenu;
 - (void)setIsContextMenu:(BOOL)flag;
 - (BOOL)canBecomeMainWindow;
+- (void)setIsArrowPanel:(BOOL)aIsArrowPanel pointingTo:(NSPoint)aArrowTip;
 
 @end
 
 @interface BorderlessWindow : BaseWindow
 {
 }
 
 - (BOOL)canBecomeKeyWindow;

--- a/widget/cocoa/nsCocoaWindow.mm
+++ b/widget/cocoa/nsCocoaWindow.mm
@@ -3710,40 +3710,94 @@ TitlebarDrawCallback(void* aInfo, CGCont
 
 - (NSString*)colorSpaceName
 {
   return NSDeviceRGBColorSpace;
 }
 
 @end
 
+@interface NSWindow(WindowAnimation)
+- (NSInteger)_orderFrontAnimationType;
+- (NSInteger)_orderOutAnimationType;
+- (id)_windowTransformAnimationForOrdering:(NSInteger)aOrdering animationType:(NSInteger)aAnimationType interruptingAnimation:(id)aInterruptingAnimation;
+@end
+
+@interface NSObject(NSWindowTransformAnimationAnchorPoint)
+- (void)setAnchorPoint:(NSPoint)aPoint;
+@end
+
+enum NSWindowTransformAnimationType {
+  NSWindowTransformAnimationPopIn = 3,
+  NSWindowTransformAnimationPopOut,
+  NSWindowTransformAnimationScaleUpAndIn,
+  NSWindowTransformAnimationScaleDownAndOut,
+  NSWindowTransformAnimationScaleDownAndIn,
+  NSWindowTransformAnimationScaleUpAndOut,
+  NSWindowTransformAnimationSpringUpAndIn,
+  NSWindowTransformAnimationFallAndFadeOut,
+  NSWindowTransformAnimationFadeIn,
+  NSWindowTransformAnimationFadeOut,
+  NSWindowTransformAnimationShake,
+  NSWindowTransformAnimationDuplicate,
+  NSWindowTransformAnimationScaleUpAndDown,
+  NSWindowTransformAnimationShadowPop
+};
+
 @implementation PopupWindow
 
 - (id)initWithContentRect:(NSRect)contentRect styleMask:(NSUInteger)styleMask
       backing:(NSBackingStoreType)bufferingType defer:(BOOL)deferCreation
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NIL;
 
   mIsContextMenu = false;
+  mIsArrowPanel = false;
+  mArrowPanelArrowTip = NSZeroPoint;
   return [super initWithContentRect:contentRect styleMask:styleMask
           backing:bufferingType defer:deferCreation];
 
   NS_OBJC_END_TRY_ABORT_BLOCK_NIL;
 }
 
 - (BOOL)isContextMenu
 {
   return mIsContextMenu;
 }
 
 - (void)setIsContextMenu:(BOOL)flag
 {
   mIsContextMenu = flag;
 }
 
+- (NSInteger)_orderFrontAnimationType
+{
+  return mIsArrowPanel ? NSWindowTransformAnimationPopIn : [super _orderFrontAnimationType];
+}
+
+- (NSInteger)_orderOutAnimationType
+{
+  return mIsArrowPanel ? NSWindowTransformAnimationFadeOut : [super _orderOutAnimationType];
+}
+
+- (id)_windowTransformAnimationForOrdering:(NSInteger)aOrdering animationType:(NSInteger)aAnimationType interruptingAnimation:(id)aInterruptingAnimation
+{
+  id animation = [super _windowTransformAnimationForOrdering:aOrdering animationType:aAnimationType interruptingAnimation:aInterruptingAnimation];
+  if (mIsArrowPanel && [animation respondsToSelector:@selector(setAnchorPoint:)]) {
+    [animation setAnchorPoint:NSMakePoint(mArrowPanelArrowTip.x, [self frame].size.height - mArrowPanelArrowTip.y)];
+  }
+  return animation;
+}
+
+- (void)setIsArrowPanel:(BOOL)aIsArrowPanel pointingTo:(NSPoint)aArrowTip
+{
+  mIsArrowPanel = aIsArrowPanel;
+  mArrowPanelArrowTip = aArrowTip;
+}
+
 - (BOOL)canBecomeMainWindow
 {
   // This is overriden because the default is 'yes' when a titlebar is present.
   return NO;
 }
 
 @end