keymasterr
commented
3 years ago I didn't find a way to detect current OS or window controls position to make my code more universal (any ideas are appreciated).
You can remove this gap manually by removing/commenting nav-bar's left margin: https://github.com/keymasterr/Firefox-UI-Theme-Tweaks-and-Bottom-Tabs/blob/a33b4417f34f00577f1af7904d7a3d6d16ea8384/userChrome.css#L18
In other operating systems, there is an unnecessary gap in front of the navigation bar. Screenshot attached:
Taken in debian unstable, using xfce desktop enviorment.