Comment 2 for bug 1626611

I’ve tested Jamie’s suggestion, but that didn’t improve things.
After some tinkering, I found that commenting out the following explicit denial in the browser profile allows access to my USB webcam:

  # QAudioRecorder needs this. We might have to allow this later, but for now
  # just silence the denial
  deny /dev/ r,

This denial is pulled in by the "microphone" policy group, and it conflicts with the camera policy group (which explicitly allows read access to /dev/).