I’ve just installed FFoA for testing 
as Vivaldi is getting slower and more bloated with every release. First impressions are very positive, esp since I have a LibreWolf desktop instance running so I can sync bookmarks and logins: I was up and running within minutes and almost everything works as I’d expect and it’s a bit sprightlier as well. I also like the availablity of extensions, great stuff for uBlock and Cookie AutoDelete!
So I’ll very probably switch to FFoA one of those days.
I have two remarks though. The tab bar from Vivaldi is sorely missed; I probably can work around that but it would a great idea if FFoA would offer something similar (possibly hidden behind an option with default off).
The second thing is more of a problem for me. I have defined dozens of keywords in my desktop bookmarks and they are a great time saver. Alas, they seem to do nothing in FFoA. No keyword support? Why is that? Esp on a mobile screen with that tiny keyboard the less I have to type the better!?