Micro-stutter on youtube on Firefox/Win 11

[haaammit]

Having some issues recently with Firefox. Been getting some really bad micro-stuttering on video playback, and it's really annoying. If I open the same video on Edge, there is no stutter, just on Firefox.
If I run in Safe mode, the issue goes away. Out of safe mode, but with all add-ons disabled the issue returns. I refreshed firefox, didn't really make much difference and was a pita reinstalling add-ons etc.
I've tried the hardware acceleration settings, makes no difference. Any ideas on where to start?
117.0 64 bit
AMD driver literally just updated 23.8.2
Win 11 2H22
I'd prefer not to use Edge, but meh, this is really bugging me now!
Ta

 

[haaammit]

TY for the reply - yes, this seems to be a new issue on existing hardware. The same video playing on Edge doesn't exhibit the same symptoms. It may or may not be related, but whilst browsing with Firefox, every once in a while there seems to be a flicker - can't really described it any better than that.
I haven't tried reducing quality as yet, nor looked at task manager. It doesn't seem to be all videos, and I haven't, as yet, noticed a pattern - will try those things next time I get the stutter/jitter.
Cheers