Kubuntu 25.10, pre-installed firefox video stuttering

[Aircorian]

Hello

I dont really know where to post this issue and the ubuntu report stuf is driving me nuts XD
TLDR:

• Problem: The pre-installed firefox version on kubuntu 25.10 has issues streaming video,
• Solution: Instal new firefox version with flatpak

long version
I run on a 1080p and a 4k monitor, when only the 4k monitor is plugged in than the original firefox works just fine.
When both monitors are plugged in the original firefox runs video's only smooth on the 1080p monitor, but when the browser is moved to the 4k monitor than the video stutter's, audio stays just fine, dragging the browser back to the 1080p monitor instantly removes the stutter and the video is smooth again.
starting the original firefox on the 4k monitor directly and only playing youtube on the 4k monitor has no effect, it stil has stutter.
newest gpu drivers have no effect, tryd installing the correct decoder but it was already installed.
i eventually just installed a different browser (librewolf) and had no issues at all.
after that i noticed i could install firefox with flatpak, installed flatpak firefox and ran that, no problems with that.
running both versions of firefox shows clearly that the original firefox has stutter while the flatpak firefox runs the video with no problems at all on the same moment.