Hmm, I use Hangouts in Firefox...
Hangouts supports WebRTC video in Firefox now, four years after supporting WebRTC in Chrome (2014-2018).
I've maintained a timeline of Hangouts' WebRTC support (as part of my work to track the sunsetting of NPAPI plugins, other than Flash, in Firefox that blocked Win64):
The chat or the video? The video hasn't worked in long time now.
Re:State of web browsers in 2018
by Wowfunhappy on Thursday December 06, 2018 @01:56PM
(#18620923)
I haven't tried Firefox, but Hangouts with video works in Safari for me.
I had to bookmark a Hangouts room URL though, which I think I opened from within GMail some time ago. If I try to just load hangouts.google.com, it won't work.
The one that still sticks in my craw is that they never bothered to add support for Hangouts in Firefox. Hangouts was modified to use WebRTC in Chrome, but relied on a plugin in Firefox--despite Firefox actually implementing the relevant WebRTC features first.