I much prefer to have the option exposed in the UI, but you can do this with any HTML5 video element by setting the video element's playbackRate. Often, it's as easy as 'document.getElementsByTagName('video')[0].playbackRate = 1.5'. I have a bookmarklet that does exactly this, so I love to see HTML5 video being the default more and more.
Re:YouTube now defaults to HTML5 video
by dublinben on Wednesday January 28, 2015 @09:31AM
(#8959970)
You should use this add-on, called YouTube All HTML5. It just works.
https://addons.mozilla.org/en-US/firefox/addon/youtube-all-h...
Also, the HTML5 player has a nice feature to change the rate at which the video plays, which makes watching long talks a lot easier.