> What did Firefox do to fix the compatibility e.g. with Teams?
I think that's the wrong way around. Why would Firefox need to change their browser for a specific web application?
Microsoft chose not to support Firefox, not the other way around. It's still choosing not to support smaller platforms (the Linux application is simply garbage, lacking basic features that have been available on other platforms for months).
When I ran into this problem, Teams didn't work because Firefox didn't allow the application to enumerate the audio devices hooked up to my computer, only exposing a "default" one. I don't even understand why that would be a problem, my browser already asked which input and output to use, why would Teams need to care?
Jitsi and Google Meet worked fine, so the problem was clearly with Microsoft's developers. They managed to fix the problem eventually, so Microsoft should take 100% of the blame here in my opinion.
I don't know about the sysadmin stuff. Honestly, with modern Chrome-clone Edge, I'd expect most business that roll out a browser to now simply stick to the built-in browser.