What I've heard is that for the most part, even x86 apps run quite well. Exceptions include weird cases like Docker (virtualization) and web browsers (JavaScript JIT), but as you say Firefox/Chromium have native updates available and Docker is working on it. Docker has no ETA though, so if you depend on that regularly it might be a temporary blocker.
For what it's worth, Rosetta 2 does claim to support JITs (which is a pretty neat trick), and the release notes for Firefox 83 claim it should work fine under Rosetta 2 on the M1.
