I'm one of those people who choose to use FF Nightly. It works with Teams unless you want to make a call or share screen - you need to change the User Agent then. I'm too lazy to do it so I'm using a phone app for calls and complaining to everyone that Teams is crap.

And I mean, it is crap by itself. It is badly thought out, it has its bad moments even on its native platform, its system of teams etc. is confusing and far inferior to the ones used by its competitors. Frankly, if it wasn't MS and their dominant market position/integration with AD, very few people would make the decision to use it for daily work. /rant