Firefox & Youtube: ERROR mp4parse] Found 2 nul bytes in "\0\0"

[peter_b]

[PROBLEM]
Since a recent update to Firefox 105.0 on Xubuntu 20.04, I can't play youtube videos anymore.

The preview image loads, and when I click the play button the video plays for like 1-4 frames, then snaps back to pause.
I ran firefox again from the console and got the following error messages:

ERROR mp4parse] Found 2 nul bytes in "\0\0"

Playback = "k key".
So, keeping "k" pressed, will play back the actual video. But basically without sound. Flickering.
A bit like a silent movie

[UPDATE]
Maybe I'm getting closer (Firefox WebDev log):

Cookie “” has been rejected by user set permissions. log_event
Cookie “CONSENT=PENDING+518; expires=Sat, 12-Oct-2024 19:23:46 GMT; path=/; domain=.youtube.com; Secure” has been rejected by user set permissions. 2 log_event

Cookie “” has been rejected by user set permissions. qoe
Referrer Policy: Ignoring the less restricted referrer policy “origin-when-cross-origin” for the cross-site request: https://rr5---sn-h0jeln7l.googlevideo.c ... xBrl4GYlA= base.js:4858:117
Referrer Policy: Ignoring the less restricted referrer policy “origin-when-cross-origin” for the cross-site request: https://r4---sn-q0c7rn76.googlevideo.co ... nq-7dOzsyX base.js2

Anyways:
Still investigating what's going on here and how to fix it...