diff --git a/widget/cocoa/nsChildView.h b/widget/cocoa/nsChildView.h
index 6c7bbf089ce0..46a0c13f552e 100644
--- a/widget/cocoa/nsChildView.h
+++ b/widget/cocoa/nsChildView.h
@@ -141,6 +141,15 @@ class APZCTreeManager;
 // format since at least OS X 10.5.
 - (void)_tileTitlebarAndRedisplay:(BOOL)redisplay;
 
+// The following undocumented methods are used to work around bug 1069658,
+// which is an Apple bug or design flaw that effects Yosemite.  None of them
+// were present prior to Yosemite (OS X 10.10).
+- (NSView *)titlebarView; // Method of NSThemeFrame
+- (NSView *)titlebarContainerView; // Method of NSThemeFrame
+- (BOOL)transparent; // Method of NSTitlebarView and NSTitlebarContainerView
+- (void)setTransparent:(BOOL)transparent; // Method of NSTitlebarView and
+                                          // NSTitlebarContainerView
+
 @end
 
 #if !defined(MAC_OS_X_VERSION_10_6) || \
diff --git a/widget/cocoa/nsCocoaWindow.mm b/widget/cocoa/nsCocoaWindow.mm
index 477368dbd6d1..d83c9050df73 100644
--- a/widget/cocoa/nsCocoaWindow.mm
+++ b/widget/cocoa/nsCocoaWindow.mm
@@ -2256,6 +2256,29 @@ nsCocoaWindow::ExecuteNativeKeyBinding(NativeKeyBindingsType aType,
   }
 
   mGeckoWindow->EnteredFullScreen(true);
+
+  // On Yosemite, the NSThemeFrame class has two new properties --
+  // titlebarView (an NSTitlebarView object) and titlebarContainerView (an
+  // NSTitlebarContainerView object).  These are used to display the titlebar
+  // in fullscreen mode.  In Safari they're not transparent.  But in Firefox
+  // for some reason they are, which causes bug 1069658.  The following code
+  // works around this Apple bug or design flaw.
+  NSWindow *window = (NSWindow *) [notification object];
+  NSView *frameView = [[window contentView] superview];
+  NSView *titlebarView = nil;
+  NSView *titlebarContainerView = nil;
+  if ([frameView respondsToSelector:@selector(titlebarView)]) {
+    titlebarView = [frameView titlebarView];
+  }
+  if ([frameView respondsToSelector:@selector(titlebarContainerView)]) {
+    titlebarContainerView = [frameView titlebarContainerView];
+  }
+  if ([titlebarView respondsToSelector:@selector(setTransparent:)]) {
+    [titlebarView setTransparent:NO];
+  }
+  if ([titlebarContainerView respondsToSelector:@selector(setTransparent:)]) {
+    [titlebarContainerView setTransparent:NO];
+  }
 }
 
 - (void)windowDidExitFullScreen:(NSNotification *)notification