Firefox is my main browser and I use Gmail daily. Can’t speak for Google Meet.
Admittedly I only use the gmail web client for viewing email and not much else, but I have never had issues with gmail on firefox. What problems are you experiencing?
The initial load takes forever, and opening emails is much slower than in a Chromium-based browser.
I use both services in librewolf and they both work ok. Gmail works just fine, meet sometimes doesn't turn on audio.