Does anyone have experience with arkenfox/user.js?

I use ArkenFox as a base for a hardened version of FF. It's not really designed to be used verbatim as that would leave the web in a fairly unusable state, at least for most users. I use a fair few overrides because on my daily browser I want it to be able to use DRM content, be able to login to my bank, etc. For me I see it as a really solid foundation, after which I can intentionally pick and choose what functionality to enable at my own risk rather than have bad defaults thrust upon me by the browser vendor.

I personally don't concern myself that heavily with attempting to defend my daily browser's fingerprint. With the default ArkenFox implementation, ResistFingerprinting in FF is enabled and that's the best you can do, but it also breaks a few things on purpose which impacts functionality. I personally have RF off and use the CanvasBlocker extension to defend against naïve fingerprinting scripts, but that's a choice users have to make.

If I were that concerned about being fingerprinted by advanced scripts, I'd be using the Mullvad Browser or TOR. Those are really the only effective way to "blend in" to a crowd. Most any browsers people use as their one for daily use that aren't either of those will be fingerprintable and identifiable by an adversary determined enough, so investing too much time in worrying about a daily browser's fingerprint beyond defending against naïve scripts isn't worth that much time investment, imo.

I've used arkenfox's firefox user profile for a good amount of time now and you're right to have some doubts about it.

No mitigation measures are foolproof and in actuality may result in you becoming more identifiable if you apply it improperly. The irony is that you're less likely to be identifiable using default settings on a default firefox instance than say enabling fingerprint resisting + ublock etc.

Privacy in the context of online browsing is achieved through obscurity. It uses techniques applied by browsers like TOR to become effective. In the case of TOR a wide adoption and it's careful implementation has made it one if not the only browser I would say offers decent privacy by default. In our case this template's usage is just a pretty insignificant fraction of the internet.

Browser fingerprinting technology is constantly evolving and uses many metrics that you may be unable to address if you're one to seek privacy. Just take it with a grain of salt. Although things may not look good for browsers nowadays. I'd say some privacy is better than no privacy at all.

I prefer librewolf