Do I need to apply user.js to Mullvas or LibreWolf browsers?

Questions
1

Do I need to apply user.js to Mullvas or LibreWolf browsers?

I mean something like Arkenfox or betterfox whatever. Will it help? Or harm?

2

You are not supposed to touch Mullvad at all with anything extra. That includes everything from user.js to extensions, to themes. As far as Librewolf goes, same thing. It does its own thing.

Also, as mentioned by the developers, Arkenfox should be used by nothing other than Firefox.

3

Do themes really affect how Mullvad Browser operates? I think I’ve read that some things can be changed if they don’t affect the fingerprint directly. For example, editing user.js or installing additional extensions is discouraged, but changing your homepage, bookmark toolbar settings, or default search engine is okay. I believe you can also disable or uninstall the Mullvad Browser Extension that comes with the browser without any worries.

Possibly relevant: About changing settings in Mullvad Browser - #5 by ruihildt

Edit: I think [1] and [2] both answer my question.