Change firefox menu color using userChrome.css
Solution 1:
This should work:
* {
background-color: red !important;
-moz-appearance: none !important;
}
Tested this on Firefox 26.0 - menus, URL bar, About dialog, etc., all show up in red.
I hope you choose a 'better' color than red. The above change will make everything red - except for content area.