I had horrible experience with Firefox preview, used it for few weeks but each week there was new bug added, not nothing fixed If you want extensions in Androi

I had horrible experience with Firefox preview, used it for few weeks but each week there was new bug added, not nothing fixed If you want extensions in Android mobile browser you can try Yandex (need to first enable through flag and install uncompressed) or Kiwi Browser (last time updated in October but feel free to compile it from source code on github) which can install extensions without jumping through the hoops, they are both better options than buggy Firefox preview.