On my daily development I came across the issue
navigator.mediaDevices is undefined when testing a website I’m developing on Firefox browser. While the fix for Google Chrome is widely known, I didn’t find anything about Firefox and decided to dig deeper myself. Turns out the fix is pretty simple.
On the address bar of Firefox type
Accept and continue
Search for insecure
media.getusermedia.insecure.enabled flag to true
That should do it!! The next time you open your website, Firefox will ask your permissions for webcam/microphone.