--- a/widget/public/nsIWidget.h
+++ b/widget/public/nsIWidget.h
@@ -97,20 +97,20 @@ typedef nsEventStatus (* EVENT_CALLBACK)
 #define NS_NATIVE_PLUGIN_PORT_CG    101
 #endif
 #ifdef XP_WIN
 #define NS_NATIVE_TSF_THREAD_MGR       100
 #define NS_NATIVE_TSF_CATEGORY_MGR     101
 #define NS_NATIVE_TSF_DISPLAY_ATTR_MGR 102
 #endif
 
-// {5FF2CD19-4F73-4935-8EA2-7A2C33166D4C}
+// {A16A3387-A529-439C-A127-A5893351FD24}
 #define NS_IWIDGET_IID \
-{ 0x5FF2CD19, 0x4F73, 0x4935, \
-  { 0x8E, 0xA2, 0x7A, 0x2C, 0x33, 0x16, 0x6D, 0x4C } }
+{ 0xA16A3387, 0xA529, 0x439C, \
+  { 0xA1, 0x27, 0xA5, 0x89, 0x33, 0x51, 0xFD, 0x24 } }
 
 /*
  * Window shadow styles
  * Also used for the -moz-window-shadow CSS property
  */
 
 #define NS_STYLE_WINDOW_SHADOW_NONE             0
 #define NS_STYLE_WINDOW_SHADOW_DEFAULT          1
@@ -639,16 +639,24 @@ class nsIWidget : public nsISupports {
      */
     virtual void GetWindowClipRegion(nsTArray<nsIntRect>* aRects) = 0;
 
     /**
      * Set the shadow style of the window.
      */
     NS_IMETHOD SetWindowShadowStyle(PRInt32 aStyle) = 0;
 
+    /*
+     * On Mac OS X, this method shows or hides the pill button in the titlebar
+     * that's used to collapse the toolbar.
+     *
+     * Ignored on child widgets and on non-Mac platforms.
+     */
+    virtual void SetShowsToolbarButton(PRBool aShow) = 0;
+
     /** 
      * Hide window chrome (borders, buttons) for this widget.
      *
      */
     NS_IMETHOD HideWindowChrome(PRBool aShouldHide) = 0;
 
     /**
      * Put the toplevel window into or out of fullscreen mode.

--- a/widget/src/cocoa/nsCocoaWindow.h
+++ b/widget/src/cocoa/nsCocoaWindow.h
@@ -230,16 +230,17 @@ public:
                         const nsTArray<Configuration>& aConfigurations);
     NS_IMETHOD DispatchEvent(nsGUIEvent* event, nsEventStatus & aStatus) ;
     NS_IMETHOD CaptureRollupEvents(nsIRollupListener * aListener, PRBool aDoCapture, PRBool aConsumeRollupEvent);
     NS_IMETHOD GetAttention(PRInt32 aCycleCount);
     virtual PRBool HasPendingInputEvent();
     virtual nsTransparencyMode GetTransparencyMode();
     virtual void SetTransparencyMode(nsTransparencyMode aMode);
     NS_IMETHOD SetWindowShadowStyle(PRInt32 aStyle);
+    virtual void SetShowsToolbarButton(PRBool aShow);
     NS_IMETHOD SetWindowTitlebarColor(nscolor aColor, PRBool aActive);
 
     // dispatch an NS_SIZEMODE event on miniaturize or deminiaturize
     void DispatchSizeModeEvent(nsSizeMode aSizeMode);
 
     virtual gfxASurface* GetThebesSurface();
 
     // be notified that a some form of drag event needs to go into Gecko

--- a/widget/src/cocoa/nsCocoaWindow.mm
+++ b/widget/src/cocoa/nsCocoaWindow.mm
@@ -1419,16 +1419,25 @@ NS_IMETHODIMP nsCocoaWindow::SetWindowSh
 
   if ([mWindow hasShadow] != (aStyle != NS_STYLE_WINDOW_SHADOW_NONE))
     [mWindow setHasShadow:(aStyle != NS_STYLE_WINDOW_SHADOW_NONE)];
   return NS_OK;
 
   NS_OBJC_END_TRY_ABORT_BLOCK_NSRESULT;
 }
 
+void nsCocoaWindow::SetShowsToolbarButton(PRBool aShow)
+{
+  NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
+
+  [mWindow setShowsToolbarButton:aShow];
+
+  NS_OBJC_END_TRY_ABORT_BLOCK;
+}
+
 NS_IMETHODIMP nsCocoaWindow::SetWindowTitlebarColor(nscolor aColor, PRBool aActive)
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NSRESULT;
 
   // If our cocoa window isn't a ToolbarWindow, something is wrong.
   if (![mWindow isKindOfClass:[ToolbarWindow class]]) {
     // Don't output a warning for the hidden window.
     NS_WARN_IF_FALSE(SameCOMIdentity(nsCocoaUtils::GetHiddenWindowWidget(), (nsIWidget*)this),
@@ -1899,17 +1908,18 @@ nsCocoaWindow::UnifiedShading(void* aInf
 }
 
 - (float)titlebarHeight
 {
   NSRect frameRect = [self frame];
   return frameRect.size.height - [self contentRectForFrameRect:frameRect].size.height;
 }
 
-// Always show the toolbar pill button.
+// Returning YES here makes the setShowsToolbarButton method work even though
+// the window doesn't contain an NSToolbar.
 - (BOOL)_hasToolbar
 {
   return YES;
 }
 
 // Dispatch a toolbar pill button clicked message to Gecko.
 - (void)_toolbarPillButtonClicked:(id)sender
 {

--- a/widget/src/xpwidgets/nsBaseWidget.h
+++ b/widget/src/xpwidgets/nsBaseWidget.h
@@ -102,16 +102,17 @@ public:
   NS_IMETHOD              SetCursor(imgIContainer* aCursor,
                                     PRUint32 aHotspotX, PRUint32 aHotspotY);
   NS_IMETHOD              GetWindowType(nsWindowType& aWindowType);
   NS_IMETHOD              SetWindowType(nsWindowType aWindowType);
   virtual void            SetTransparencyMode(nsTransparencyMode aMode);
   virtual nsTransparencyMode GetTransparencyMode();
   virtual void            GetWindowClipRegion(nsTArray<nsIntRect>* aRects);
   NS_IMETHOD              SetWindowShadowStyle(PRInt32 aStyle);
+  virtual void            SetShowsToolbarButton(PRBool aShow) {}
   NS_IMETHOD              HideWindowChrome(PRBool aShouldHide);
   NS_IMETHOD              MakeFullScreen(PRBool aFullScreen);
   virtual nsIRenderingContext* GetRenderingContext();
   virtual nsIDeviceContext* GetDeviceContext();
   virtual nsIToolkit*     GetToolkit();  
   virtual gfxASurface*    GetThebesSurface();
   NS_IMETHOD              SetModal(PRBool aModal); 
   NS_IMETHOD              SetWindowClass(const nsAString& xulWinType);

--- a/xpfe/appshell/src/nsXULWindow.cpp
+++ b/xpfe/appshell/src/nsXULWindow.cpp
@@ -989,16 +989,17 @@ void nsXULWindow::OnChromeLoaded()
     // (however, we think the benefits of intelligent dependent window placement
     // trump that override.)
     if (!parentWindow)
       positionSet = PR_FALSE;
 #endif
     if (positionSet)
       positionSet = LoadPositionFromXUL();
     LoadMiscPersistentAttributesFromXUL();
+    LoadToolbarButtonPresenceFromXUL();
 
     //LoadContentAreas();
 
     if (mCenterAfterLoad && !positionSet)
       Center(parentWindow, parentWindow ? PR_FALSE : PR_TRUE, PR_FALSE);
 
     if (mShowAfterLoad)
       SetVisibility(PR_TRUE);
@@ -1431,16 +1432,29 @@ NS_IMETHODIMP nsXULWindow::LoadIconFromX
   if (id.IsEmpty()) {
     id.AssignLiteral("default");
   }
 
   mWindow->SetIcon(id);
   return NS_OK;
 }
 
+NS_IMETHODIMP nsXULWindow::LoadToolbarButtonPresenceFromXUL()
+{
+  nsCOMPtr<nsIDOMElement> windowElement;
+  GetWindowDOMElement(getter_AddRefs(windowElement));
+  NS_ENSURE_TRUE(windowElement, NS_ERROR_FAILURE);
+  nsAutoString attr;
+  nsresult rv = windowElement->GetAttribute(NS_LITERAL_STRING("toggletoolbar"), attr);
+  if (NS_SUCCEEDED(rv)) {
+    mWindow->SetShowsToolbarButton(attr.LowerCaseEqualsLiteral("true"));
+  }
+  return NS_OK;
+}
+
 NS_IMETHODIMP nsXULWindow::SavePersistentAttributes()
 {
   // can happen when the persistence timer fires at an inopportune time
   // during window shutdown
   if (!mDocShell)
     return NS_ERROR_FAILURE;
 
   nsCOMPtr<nsIDOMElement> docShellElement;

--- a/xpfe/appshell/src/nsXULWindow.h
+++ b/xpfe/appshell/src/nsXULWindow.h
@@ -117,16 +117,17 @@ protected:
    void StaggerPosition(PRInt32 &aRequestedX, PRInt32 &aRequestedY,
                         PRInt32 aSpecWidth, PRInt32 aSpecHeight);
    PRBool     LoadPositionFromXUL();
    PRBool     LoadSizeFromXUL();
    PRBool     LoadMiscPersistentAttributesFromXUL();
    nsresult   LoadChromeHidingFromXUL();
    NS_IMETHOD LoadWindowClassFromXUL();
    NS_IMETHOD LoadIconFromXUL();
+   NS_IMETHOD LoadToolbarButtonPresenceFromXUL();
    NS_IMETHOD SavePersistentAttributes();
 
    NS_IMETHOD GetWindowDOMWindow(nsIDOMWindowInternal** aDOMWindow);
    NS_IMETHOD GetWindowDOMElement(nsIDOMElement** aDOMElement);
 
    // See nsIDocShellTreeOwner for docs on next two methods
    NS_HIDDEN_(nsresult) ContentShellAdded(nsIDocShellTreeItem* aContentShell,
                                           PRBool aPrimary, PRBool aTargetable,