about this:

This userchrome / config

• Brings back compact mode (Firefox 89)
• Removes Unified extensions menu (thing firefox copied from google... a bit late)
• Hide Firefox login (email address)

shoutout

https://www.userchrome.org/firefox-89-styling-proton-ui.html#compactmode
https://ffprofile.com/ - https://github.com/allo-/firefox-profilemaker
https://github.com/arkenfox/user.js
https://github.com/AveYo/fox
https://github.com/yokoffing/Betterfox
https://github.com/Endor8/userChrome.js
https://github.com/black7375/Firefox-UI-Fix
https://gitlab.com/postmarketOS/mobile-config-firefox/-/tree/master
and few more resources im trying to remember

install:

about:profiles

find default profile, on Root Directory find open folder button, add files which this repo provides.

restart firefox.