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YouTube Choppy/Slo-Mo Playback in 4K Since Firefox 149

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YouTube is playing 4K videos like they are in slow motion. If I lower the quality they work fine, but switch back to 4K and it's slow motion stutter-fest again. I have seen several topics about this but it's still happening to me despite all of the "fixes" I've tried. This is a list of everything that I've seen and tried, and not a single one or any combination of them fixes the problem for me.

In about:config I tried changed the following to False: gfx.webrender.layer-compositor media.av1.enabled media.wmf.dxva.d3d11.enabled

Tried uninstalling all extensions.

Tried a complete uninstall and reinstall of 149.0.2 with a fresh profile instead of updating from 148.0.2.

Tried installing uBlock Origin and used the following rule: ||www.youtube.com/web-reports$xhr

Tried unchecking the uBlock "Quick Fixes" filter.

Tried disabling hardware acceleration.

Tried disabling DNS Over HTTPS.

All that said... what DID fix it was reverting back to Firefox 148.0.2. I tried again to update from that to 149.0.2 using the FF built in updater but the same issue immediately came back. Zero issues at all playing 4K YouTube videos on FF 148.0.2 or the latest versions of Chrome and Edge. Issue is ONLY on FF 149 and 149.0.2.

YouTube is playing 4K videos like they are in slow motion. If I lower the quality they work fine, but switch back to 4K and it's slow motion stutter-fest again. I have seen several topics about this but it's still happening to me despite all of the "fixes" I've tried. This is a list of everything that I've seen and tried, and not a single one or any combination of them fixes the problem for me. In about:config I tried changed the following to False: gfx.webrender.layer-compositor media.av1.enabled media.wmf.dxva.d3d11.enabled Tried uninstalling all extensions. Tried a complete uninstall and reinstall of 149.0.2 with a fresh profile instead of updating from 148.0.2. Tried installing uBlock Origin and used the following rule: ||www.youtube.com/web-reports$xhr Tried unchecking the uBlock "Quick Fixes" filter. Tried disabling hardware acceleration. Tried disabling DNS Over HTTPS. All that said... what DID fix it was reverting back to Firefox 148.0.2. I tried again to update from that to 149.0.2 using the FF built in updater but the same issue immediately came back. Zero issues at all playing 4K YouTube videos on FF 148.0.2 or the latest versions of Chrome and Edge. Issue is ONLY on FF 149 and 149.0.2.

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