User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:62.0) Gecko/20100101 Firefox/62.0 Steps to reproduce: I wrote some RTC code and opened it in firefox, I then opened Responsive Design mode and reloaded the page. Actual results: In normal mode the promise is fulfilled and the offer is created (you can see in the console) In RDM, the promise is never fulfilled. Expected results: The offer should be created in RDM

I can confirm this. I also see this in the browser console (where chrome errors show up): > aMessage.target.contentPrincipal is undefined webrtcUI.jsm:206 [1] > receiveMessage resource:///modules/webrtcUI.jsm:206:11 > receiveMessage jar:file:///usr/lib/firefox-trunk/browser/omni.ja!/components/nsBrowserGlue.js:257:30 > receiveMessage self-hosted:1031:17 Not sure why we wouldn't have a principal there, but this seems more like an issue with responsive design mode than with our webrtc implementation. Moving to the RDM component. [1] https://searchfox.org/mozilla-central/rev/924e3d96d81a40d2f0eec1db5f74fc6594337128/browser/modules/webrtcUI.jsm#206