Better Fix for Firefox Tab Styling

Setting up a new machine, I was reminded that the default Firefox tab style after 89 is “utter lack of visual separation, but with lots of useless empty space.” I’ve hacked sloppy solutions on several other machines, but it looks like the nice way going forward is a config generator from the userchrome folks to generate a userChrome.css that restyles the tab buttons with only a bit of screwing around and no options scheduled for deprecation.