appMenu.css: Adjust appMenu.css for Firefox 127

Firefox 127 introduced some changes to appMenu.

This MR fixes these, and also makes room for the Translate button introduced with FF 118, so that the appMenu does not show a scroll bar by default going forward (FF 128 will be the next ESR).

Testing went fine. On Sxmo there's still a scroll bar, but as "Quit" can be tapped without scrolling, I will not change a thing. I think this is due to font-related settings that users my have changed to whatever they prefer, so this is fine — if not reassuring: The scrollbar shows up in FF 127, which it does not do with the current release/master.