Vanilla WebRTC in its current form is still too unstable to actually be usable for production video chat applications. Its limitations affect all of the leading commercial providers: Tokbox, Twilio, Agora, etc.
For example, on MacOS, there is a severe breaking CoreAudio bug in WebRC that hasn't been fixed for over 3 years which affects 8% of users by causing unmuted microphones to not transmit any audio [1]. We've never seen this problem come up with Hangouts though.
iOS builds for Google's WebRTC libjingle_peerconnection library have been broken for over 2 months, too [2].
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Firefox is ending support for plug-ins, so Hangouts won’t be able to support video and phone calls in Firefox until Hangouts is updated to resolve the problem. Google is working on a solution. Google presents that help where a video error occurs with a WebRTC-compatible browser, which seems wrong to. Because Google Hangouts in Firefox currently relies on browser plugins to enable video and audio calls, users of Hangouts will not be able to make audio or video calls in the upcoming Firefox 52 release. Google is actively working to develop a solution that will enable Hangouts to work in Firefox without a plugin. In the meantime, we recommend. As Mike Williams stated in a March 1, 2017 email: Google announced late last week that Google Hangouts will not work with the next release of the Firefox browser (Firefox 52) coming on March 7. Hangouts relies on plugins to enable video and audio calls, and Firefox has announced that it would end support for browser plugins on it’s 52 release to help improve performance and security.
It's no surprise that there is some core Hangouts team within Google building something else. Even Google's own AppRTC 'reference' application implementation has some seriously questionable design decisions in its code (such as sending signaling messages to Google App Engine to forward over websockets).
Google needs to figure out how to bridge the gap between both organizations so that everyone can benefit from the stability gains made by the Hangouts team.
Google Hangouts Firefox Plugin
[1] https://bugs.chromium.org/p/webrtc/issues/detail?id=4799
Google Hangouts Firefox
[2] https://github.com/pristineio/webrtc-build-scripts