stuttering in full screen videos on Firefox with VRR enabled

[michaelBelsanti]

When viewing any video in Firefox, it will become significantly more choppy when full screened, after the video controls disappear. It is completely smooth while in windowed mode, or while the video controls are visible. This only happens while VRR is set to automatic or always.

It does not affect Chromium browsers, and it does not occur with VRR enabled on Plasma 6. It also doesn't affect other video players.

This video can be used to demonstrate the issue if it is occuring: https://youtu.be/FVNO-ehIOdw

System info:
NixOS 25.05
COSMIC Comp rev - 9dddead

AMD 7800X3d
AMD 7800XT

[michaelBelsanti]

possibly related - https://bugzilla.mozilla.org/show_bug.cgi?id=1879271