Firefox: How to enable userChrome and userContent CSS files? (Linux)
New Firefox for the last couple of years are less customizable before, and many things are hidden from the human eye. Nowadays even giving CSS file for the browser (userChrome.css) or content (userContent.css) is hidden, and doesn't show default. Even if these files are in the right place, Firefox simple doesn't see them.
Note: this works for any Firefox fork, and even Tor Browser, but you have to check the profile directory. Also this should work on Windows too, but I don't know where are those directories, so I
Where to put the CSS files?
On Linux, Firefox uses the ~/.mozilla/firefox directory in the home folder to contain the profile directories, which usually are "somecharacters.default", unless you manually created the profile yourself. You can only see that directory if you turn on hidden files in your file manager. In that profile folder you need to create a chrome directory.
For example: ~/.mozilla/firefox/eb12ui1ww3.default/chrome
In that directory you can create the userChrome.css and userContent.css files, both are case sensitive in name.
For LibreWolf, the profile directory is directly under ~/.librewolf, while for Tor Browser it is "Browser/TorBrowser/Data/Browser/profile.default".
How to enable userChrome files?
To enable these files again, type about:config in the URL bar, and click on the "Accept the Risk and Continue" button.
You will see another search bar, and copy this into it:
It will show you one result, and you will see one button at the end of that line, click on it, so false turns into true. Restart your browser, and it will see the files, if they are in place.