From my perspective, none of them. The browser is reasonably fast, and you can still share bookmarks and logins with other installations if you create a Mozilla account (or host your own sync server!).

But, from my perspective, just having uBlock Origin installed in the extensions is a huge differentiator, that gives most pages a lot of speedup. Stylus can also be helpful to fix some suboptimal mobile designs.

One of the things that annoys me on a daily basis is how FF handles the address bar. In Brave, if I click on the address bar. It gives me a button to copy the link. If I have a link copied, there's a paste button. If I use FF, I have to go through the whole monkey dance of clicking on the address bar, tap holding the address until the copy menu shows up, then I can copy.

Then there's absolutely infuriating stuff like the address bar and tabs disappearing when scrolling, which is fine, but it can be really fucking annoying trying to get it to show up again. It doesn't respond properly, sometimes I'll have to scroll back up a whole page before it does anything and all I wanted to do was switch tabs, so I have to scroll back down when I come back. Makes me want to punch an FF developer.