In Firefox fullscreen not working.

[przemsiedl]

Expected behaviour

When I enabled fullscreen mode video should be stretched.

Actual behaviour

The video on the first screen works correctly.

but on fullscreen looks like this

Variables

1. Browser version Mozilla Firefox 87.0 (64 bit) on windows 10 20h20 19042.867 Education
2. Arch Linux Firefox version 86.0.1 (64 bit) problem is the same.

[g6094199]

+1

on FF and Edge4Linux