Make the menu of firefox-esr 78 look good on mobile
postmarketos-config-firefox package is optimized for firefox-esr 68, which is what Alpine was shipping in Alpine 3.12 (and therefore it's available when installing postmarketOS on the stable channel). The menu looks like in the first screenshot and is quite usable. However, that version of Firefox is becoming EOL soon, so Alpine 3.12 will soon ship (or is already shipping) firefox-esr 78, on which the menu doesn't look good.
From quick online research, firefox seems to be very customizable through userchrome.css, so we can probably just ship such a file that makes the menu work well again for our mobile use case.