@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

menuitem[oncommand="objmenuGlobal.openConfigWindow();"] { 
    list-style-image: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAgY0hSTQAAeiYAAICEAAD6AAAAgOgAAHUwAADqYAAAOpgAABdwnLpRPAAAABh0RVh0U29mdHdhcmUAUGFpbnQuTkVUIHYzLjEwcrIlkgAAAjBJREFUOE9tUz9oE1EcfpUbghxFJIhIKA7iUIJDhw4hOIRDpASnTlI6lIwdSilOpUM5OkgoUkqm4pSpSOgQMoTDQTKFh9NDihxOR3E4isMhUg4/v9+73plrG3jh8bvf932/P9+bS/+m6ubvZ/cD/pyfq19nZ0q5FfXAe60qz56qx1tbSlUqc6V8IchPMg6g77uI9naRfA9RxL9qRPs+9MMq4tGwiFvxPCk67MK8bCK9+k84Sy73hET6ngPJzb9ZAlG24N+JiqZ9kiQF8SyJWawjvYyV5CbXlSiCbNmiHI52YE5XER51EA1INNOeaRD0ZZLFmJtjVPS+m/V8oQleg9n3YJYdTJZ4GjWS+TCvPMS94xKhzCQ68KHCjQ6SKYc0PbHquuUS4CIekPRHgPBdh8NzoN/UEfX8YkbJNwPBKr1Qs8zRZyr12lY5fMvYRcA++zBLdYTbTZI6MK2ssnB7FfH4E/SjKgn4JwTmYxvhaBOTF0yU5BUXet5lBW17tzGeYcPBCUn00S70k9p1CyxHWojGm9ArVduClC2zEFUB9Qk6Jrmc7qKDYIPDXl9DMUQhCAcc4l6TpTFhIVPKAQLyn5NovY2Ag9UEywLsvvOVmNMOCTwM57Nke5arCA52oG+s1WLom5KRZBum5dnpDw99JJdxaXW5L2wOzXfLymJTOu1OUG4gcaGUXrJy8WhoT3kwYhLxfRHnwxKzyVZy5TsJbJDWFgWZsHhECOVuVa/SW9X9A1gEnAGJsRGTAAAAAElFTkSuQmCC") !important;
}