--- a/widget/cocoa/nsCocoaWindow.h
+++ b/widget/cocoa/nsCocoaWindow.h
@@ -394,14 +394,15 @@ protected:
                                                 // (MakeFullScreen() call) to EnteredFullScreen()
   bool                 mModal;
 
   bool                 mUsesNativeFullScreen; // only true on Lion if SetShowsFullScreenButton(true);
 
   bool                 mIsAnimationSuppressed;
 
   bool                 mInReportMoveEvent; // true if in a call to ReportMoveEvent().
+  bool                 mInResize; // true if in a call to DoResize().
 
   int32_t              mNumModalDescendents;
   InputContext         mInputContext;
 };
 
 #endif // nsCocoaWindow_h_

--- a/widget/cocoa/nsCocoaWindow.mm
+++ b/widget/cocoa/nsCocoaWindow.mm
@@ -30,16 +30,17 @@
 #include "nsCocoaFeatures.h"
 #include "nsIScreenManager.h"
 #include "nsIWidgetListener.h"
 #include "nsIPresShell.h"
 
 #include "gfxPlatform.h"
 #include "qcms.h"
 
+#include "mozilla/AutoRestore.h"
 #include "mozilla/BasicEvents.h"
 #include "mozilla/Preferences.h"
 #include <algorithm>
 
 namespace mozilla {
 namespace layers {
 class LayerManager;
 }
@@ -107,16 +108,17 @@ nsCocoaWindow::nsCocoaWindow()
 , mWindowMadeHere(false)
 , mSheetNeedsShow(false)
 , mFullScreen(false)
 , mInFullScreenTransition(false)
 , mModal(false)
 , mUsesNativeFullScreen(false)
 , mIsAnimationSuppressed(false)
 , mInReportMoveEvent(false)
+, mInResize(false)
 , mNumModalDescendents(0)
 {
 
 }
 
 void nsCocoaWindow::DestroyNativeWindow()
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
@@ -1328,20 +1330,23 @@ NS_METHOD nsCocoaWindow::MakeFullScreen(
 // Coordinates are global display pixels
 nsresult nsCocoaWindow::DoResize(double aX, double aY,
                                  double aWidth, double aHeight,
                                  bool aRepaint,
                                  bool aConstrainToCurrentScreen)
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NSRESULT;
 
-  if (!mWindow) {
+  if (!mWindow || mInResize) {
     return NS_OK;
   }
 
+  AutoRestore<bool> reentrantResizeGuard(mInResize);
+  mInResize = true;
+
   // ConstrainSize operates in device pixels, so we need to convert using
   // the backing scale factor here
   CGFloat scale = BackingScaleFactor();
   int32_t width = NSToIntRound(aWidth * scale);
   int32_t height = NSToIntRound(aHeight * scale);
   ConstrainSize(&width, &height);
 
   nsIntRect newBounds(NSToIntRound(aX), NSToIntRound(aY),