> IceCat 60.2.0-esr

What is "esr"?  I have IceCat 60.2.0-gnu, would that make a difference?

> I tried
> typing in "test" and hit "go", and it asked me for permission to use the
> microphone and camera.

This is the expected behaviour.  On my end, I have a grey background and nothing
else.  No popup.

> since I don't really
> know what that website or jitsi is about, although I see that (at least
> some parts of jitsi) are free software, which is nice to know.

It is free software (Apache license) as far as I know.
You can run your own instance if you like.  Jitsi has been one of the best VoIP
experience I've had.

-- 
Pierre Neidhardt
https://ambrevar.xyz/