As a user who's tested Firefox Preview and loved extension support in Firefox for Android: it's been good enough for me to have somewhat naturally transitioned to using it as my main browser. The built-in tracking protection blocks practically everything that I used uBlock Origin for (though I'd still appreciate the real thing coming), I haven't really experienced bugs, and it's really quite snappy.

There's certainly still a number of features missing (I'm personally eagerly awaiting the return of the home screen), but it's certainly not as dire as some here make it sound, and it's been progressing pretty rapidly.