Hi, I have a laptop and connected additional monitor. FF works normally until I move the floating video window to another monitor. Then it 'rescales' itself, the floating video changes ratio and can't be in full screen. When I move back to FF and want to make a normal full video (YouTube) I don't see anything because I can see using alt+tab that FF minizes itself to the most smaller window. The full screen youtube video also is just a fraction of the full screen - I can see the scroll bars but there is no way to extend it to full monitor. To reset it I have to switch off FF or alt+tab, then windows+arrow to make other program to occupy for example half the screen and chose FF to feel the rest and then extend and full screen again.

It's only happening with connected monitor that extends my monitor.