Firefox 71 has stopped parsing the legacy
rid= parameters in WebRTC simulcast attributes. The new format supported since Firefox 68 only requires a RID, so, for example,
a=simulcast: send rid=8 recv rid=9
has to be
a=simulcast: send 8 recv 9
Currently, video calls in Google Hangouts Meet and Whereby are broken due to this change.
Update: This change has been reverted in Firefox 71 to give services more time to adopt the new behaviour. Mozilla developers are planning to redo the change with Firefox 72.
Update 2: The change has been landed again to Firefox 72 after both Google and Whereby fixed their issue. If you run a similar service, please be sure to test it.