It works on Chrome, but somehow it doesn't work on Firefox..
How can I get YouTube to play at 2x speed in Firefox, in addition to Chrome?
youtube
You can play a YouTube video at twice its speed on Chrome because you're using an HTML5 <video> player. It's almost always automatic on Chrome because Chrome seems to support everything the player needs:HTMLVideoElement, H.264, WebM VP8, Media, Source Extensions, MSE & H.264, MSE & WebM VP9.FireFox, on the other hand, only supports the first half:Hence the player is rarely an HTML5 video object.However, you can turn it on manually. Go to http://www.youtube.com/html5, and click on the blue Request the HTML5 player button:You can later click Use default player if you have any problems. However, you should now be able to change the speed of most of your videos like in Chrome: