Bug 880124 - Make -moz-mac-fullscreen-button 0px wide on 10.6, which doesn't have a fullscreen button. r=smichaud

widget/cocoa/nsNativeThemeCocoa.mm

@@ -2766,9 +2766,11 @@ nsNativeThemeCocoa::GetMinimumWidgetSize(nsRenderingContext* aContext,
     }
 
     case NS_THEME_MOZ_MAC_FULLSCREEN_BUTTON: {
+      if ([NativeWindowForFrame(aFrame) respondsToSelector:@selector(toggleFullScreen:)]) {
         // This value is hardcoded because it's needed before we can measure the
         // position and size of the fullscreen button.
         aResult->SizeTo(20, 0);
+      }
       break;
     }