Chrome has a baked-in plugin for Hangouts. They used to have you install a plugin for Firefox, but since Firefox has removed NPAPI in version 52 it no longer works. Supposedly they are working on a standards-based solution.

https://gsuiteupdates.googleblog.com/2017/02/google-hangouts...

The cynic in me things this is a case of "We use chrome so we developed for chrome - we'll fix other browsers later" (Yes I'm bitter about the state of the cross-browser development sometimes)

I don't know for sure, but I suspect the key to success in videoconferencing is doing really extensive testing.

The users are going to try to transition from NATed-mobile-data to corporate-wifi-with-ssl-mitm while reinserting their USB headset and connecting an external monitor while screensharing with participants running five different OSes.

Maybe they've had time to do all that testing on Chrome, but they haven't got around to it yet with Firefox.

Possibly the same thing that powers Hangouts and requires to install plugin in other browsers (as other browsers don't support plugins anymore, Hangouts works only in Chrome too).