Facebook and Messenger call Camera and Microphone permission not turning on
If I try to make a voice call on Messenger Facebook through Firefox (version 81.0) it asks permission for microphone as usual and after allowing, it works perfectly. However, whenever I try to make a Video Call for the first time, there does comes up a prompt request asking permission for both Microphone and Camera. No matter I allow for once or put a tick on the 'Remember choice for this website', the prompt pop-up closes but the black screen by Facebook/Messenger with the instruction telling to allow both the camera and Microphone (see the screenshot attached) still stays as it is and I can't get to the call at all! Also, after closing and reopening Firefox and when trying to call again, the prompt does not come up anymore, leaving me stuck at the instruction page.
The problem of no prompts can be fixed by ending the task of Firefox from the task manager, but then again after reopening and calling again, after allowing those permissions once more, it gets stuck at the instruction page again!
It would be very helpful if someone could kindly share the solution to this problem. Thanks!