the most useful extensions for android firefox - ublock origin, there is already (and many more). Also, mozilla is working on bringing all desktop add-ons to mobile and everyone can contribute.
I’m not sure if using Librewolf on desktop or Mull on mobile counts but they are pretty good hardened forks of Firefox.
Firefox is great but the downside is that it isn’t as private as browsers I’ve mentioned by default. Still, it is solid choice from privacy perspective.