--- a/toolkit/xre/MacApplicationDelegate.mm
+++ b/toolkit/xre/MacApplicationDelegate.mm
@@ -240,19 +240,22 @@ static NSWindow* GetCocoaWindowForXULWin
   while (NS_SUCCEEDED(windowList->HasMoreElements(&more)) && more) {
     // Get our native window
     nsCOMPtr<nsISupports> xulWindow;
     rv = windowList->GetNext(getter_AddRefs(xulWindow));
     NS_ENSURE_SUCCESS(rv, nil);
     NSWindow *cocoaWindow = GetCocoaWindowForXULWindow(xulWindow);
     if (!cocoaWindow) continue;
     
+    NSString *windowTitle = [cocoaWindow title];
+    if (!windowTitle) continue;
+    
     // Now, create a menu item, and add it to the menu
     NSMenuItem *menuItem = [[NSMenuItem alloc]
-                              initWithTitle:[cocoaWindow title]
+                              initWithTitle:windowTitle
                                      action:@selector(dockMenuItemSelected:)
                               keyEquivalent:@""];
     [menuItem setTarget:self];
     [menuItem setRepresentedObject:cocoaWindow];
 
     // If this is the foreground window, put a checkmark next to it
     if (SameCOMIdentity(xulWindow, frontWindow))
       [menuItem setState:NSOnState];