Not exactly a guide but there is this wonderful github repo.

Some advice to give it a try: Open firefox (desktop only) in the search box type about:profiles and create a new profile to put the user.js in without affecting your main profile.

This github repo is rather complex and there is alot to read and grasp, but it’s a very good starting point to harden your firefox.

You can also give a look at the arkenfox user.js.

Those are complex user.js but you can produce your own with the tweaks you need, in case you need video confercence or what else.