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Makes YouTube videos run in high definition + YouTube fixes
< Feedback on YouTube HD Override
From what I can tell, you have to be using the HTML5 player for the setting to take effect. Try going here to see if you're currently using the HTML5 player. You should be...
Disables DASH playback dose not work？
Firefox 38.0.5b3
YouTube HD Override 2.8.2
The youtube is still work by dash playback.