http://www.ghacks.net/2014/10/26/the-state-of-media-source-extensions-in-firefox/ http://www.ghacks.net/2014/10/26/the-state-of-media-source-e... TL;DR: For no

http://www.ghacks.net/2014/10/26/the-state-of-media-source-extensions-in-firefox/ http://www.ghacks.net/2014/10/26/the-state-of-media-source-e... TL;DR: For now you need to use beta/aurora/nightly releases of firefox to enable 1080p/4K youtube with the HTML5 player.