Quality stuck at 360p for all videos

[Pikachuy]

This happened out of the blue, along with the player malfunctioning. I fixed the player problem (the video stuck to the left side) by installing the Developers build, but now the quality is stuck at 360p.

I'm using Firefox 34.0.5 and I upgraded to 35.0.1, but videos didn't work at all in that version, with or without Youtube Center. Is Youtube screwing around the HTML5 or something?

[Zarggg]

In Firefox 35 (and the current 36 beta), MSE (Media Source Extensions -- a required browser component for the HTML5 player) is disabled by default. The intended function is for Firefox to use the Flash player until the MSE implementation is developed further (I haven't read the Firefox tickets in detail, but from what I understand, there are still some bugs that must be fixed prior to being acceptable for release).

If you wish to use the HTML5 player, change the preference media.mediasource.enabled to true in about:config then restart Firefox.

[Piter432]

And create a boolean line called "media.mediasource.ignore_codecs" (Windows 7 and higher required) setted to "true".

[Yonezpt]

Remember that forcing mediasource in the latest Firefox stable version will have negative results in terms of performance. If you truly wish to use HTML5 correctly in Firefox perhaps it would be best for you to use the Nightly version which is already fully capable of playing HTML5 in YouTube.

[Lucatir]

Developer Edition should also suffice. Or so it seemed last I used it before switching to another browser.

[mikewinq]

Try deleting all your cookies from Google and Youtube! It worked for me!