At first it was great, I had nice smooth 1080p playback on youtube, but now, for some reason, the max resolution I can set is 480p, and I don't understand why.

Does not work in Firefox. It can be seen from the power consumption, processor load and lags. Radeon HD7560D video card. Everything works fine in Chrome, EDGE decodes (informs) on n 264 by default. There may be a problem in the browser itself.