dotfiles/.config/firefox/README.md

Symlink the file to the profile directory:
```
ln -s ~/.config/firefox/userjs ~/.mozilla/firefox/[PROFILE]/chrome/user.js
ln -s ~/.config/firefox/userChrome.css ~/.mozilla/firefox/[PROFILE]/chrome/userChrome.css
```
in about:config
```
toolkit.legacyUserProfileCustomizations.stylesheets auf true setzen
```