Fennec is what I use. Full extension support etc.

Edit: re-reading this thread I decided to double check exactly where Fennec stands in relation to Firefox for Android. The main purpose of Fennec is to remove built in telemetry and proprietary shit.

As I understand it, this means they do tend to keep annoying / waste of time "enhancements" and features in base Firefox, so long as those features can be used with libre (or at least self-hostable) alternative services. So it is basically unopinionated about whether changes to Firefox are good or bad, just whether they can be used without connecting to Mozilla cloud / api shit.

This is arguably what we want most of the time, since you can just not use the features you don't like, but I'm not sure what the implications will be when AI shit gets more tightly integrated.

HOPEFULLY the Fennec team will understand that this proposed AI shit inherently compromises browser privacy, since it adds a layer of built in surveillance by design which, even if you could "swap out" the AI backend, given Firefox's fairly shithouse security would make an architectural change like this into an attack surface with very risky implications for privacy.

Time will tell.