I use FireFox quite some time on my iMac. With the version V89.0.1 I have problems with FaceBook Messenger videochat. The screen of the partner stays black. I only see my own little video screen on a black screen. Normally after allowing my camera and my mike to be used I get a message: Calling And when answered the other partner shows up on large screen. Now the text is different : Something like : Waiting for other partner to join. And the large screen stays black. The other partner can see and hear me. I tried with another browser (Brave) and then all functions well. But Brave doesn't support the Picture-in-Picture function that FireFox has. Till last week I could use the Picture-in-Picture function in Messenger Videochat. It was great to have the minimized video screen of the videopartner on top of all other programs I open.