That’s both disheartening and good to know. IMHO FF wastes too much vertical and horizontal space in the bars at the top of the page. I always liked being able to shrink those down, hopefully they will continue to support it

The only way I know of, is to restart Firefox. If you’re concerned whether or not FF is picking up your changes (I always forget which profile directory is being read (AppData vs Local) on windows) you could try something like this:

/*** uncomment below to verify userChrome.css is being read by turning the taskbar red /
/ #nav-bar{ background: #f00 !important } ***/

Just uncomment the 2nd line, restart FF with your changes, and comment it out once you’re done