@-moz-document url("chrome://browser/content/browser.xul") {

#toolbar-menubar menupopup {
direction: rtl !important;
-moz-transform: scaleX(-1);
}

#toolbar-menubar menupopup menuitem,
#toolbar-menubar menupopup menu {
direction: ltr !important;
-moz-transform: scaleX(-1);
}

}