I also have some memory of asking all participants in Jitsi meetings to not use firefox, because the call would start to lag for all participants if bandwidth was an issue for the firefox users in the call. Don't know if that is still the case or not though.
If you read to the end, it looks like the expected underlying reason is now fixed, but it hasn't been confirmed yet whether it resolved the problem. If someone knows how to reproduce, they could try it out and comment there.
I also have some memory of asking all participants in Jitsi meetings to not use firefox, because the call would start to lag for all participants if bandwidth was an issue for the firefox users in the call. Don't know if that is still the case or not though.