I use FireDragon, because it’s the only browser I could find that has a vertical tab-bar that collapses. Supposedly Zen does it, too, but I couldn’t get it to work.
FireDragon also has a toolbar to the side with a notepad and other neat stuff. I haven’t used that yet, but it could be cool.
Fennec on mobile, haven’t gotten around to replacing FF on Desktop yet.
Should we also be comparing rendering engines?
Librewolf, it’s Firefox but without the evil.