When I click an organizer's join link, FF attempts to resolve the request, but the cycle icon just cycles endlessly. I think it's trying to open the app, but I'm never prompted.
When I open the URL in MS Edge, I'm asked to open the app, which I accept, and then I can join the meeting.
FireFox 78.0.2 (64-bit). I have tried turning off enhanced tracking protection w/o any success. I have been able to open RC links in FF previously, though I don't know when it stopped working.