Video playback is partially broken on Linux for resolutions above 720p. As can be seen in the attached screenshot only part of the rendered video gets updated every frame.
After bisecting I found these changesets. It seems to me that the most likely candidate is bug 1677293.

Switching to full screen resolves the issue until exiting full screen playback and moving the cursor over the frozen parts causes them to update as long as the cursor moves.

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

Thanks for finding a regression range! I'm going to move this based on the details in comment 0. As a further check, can you navigate to about:config and check if setting the gfx.webrender.force-disabled pref to true impacts the issue?

(In reply to Bryce Seager van Dyk (:bryce) from comment #2)

As a further check, can you navigate to about:config and check if setting the gfx.webrender.force-disabled pref to true impacts the issue?

Force-disabling WebRender does indeed resolve the issue.

I just saw that there already seems to be an appropriate bug for this with bug 1678954, so I guess this can be marked as duplicate and closed.

Set release status flags based on info from the regressing bug 1677293