[AShyFig]

I did some more digging just now since this was bugging me so much. Behavior persisted after restarting firefox.

Under firefox settings/site permissions the microphone is "Blocked by Android"

So I decided to double check my android settings, and was greeted by some splash page explaining what the permissions settings page was for. (Perhaps this page appeared after a recent update?)

After clearing the page I see Firefox microphone permissions sitting in the "ask every time" catagory. Im 100% sure i did not get asked or give permission for microphone usage.

I go back to Firefox and YouTube no longer accesses my microphone when playing a video. The only variable I can think of was clearing that splash page. Mysterious. :)