Here's my general-purpose speed-adjustment bookmarklet:

    javascript:void%20function(){document.querySelector(%22video%22).playbackRate=parseFloat(prompt(%22Set%20the%20playback%20rate%22))}();

And I find that about +70% is the speed I most-frequently want, so here's my one-click "x1.7":

    javascript:void%20function(){document.querySelector(%22video%22).playbackRate=1.7}();

Both of these adjust the speed of all non-iframe-embedded HTML5 video elements on the current page.

Of course, because of XSS-prevention rules, they won't help with iframe-embedded players. For that I guess you're gonna need a plugin.

`queySelector` only returns the first matching element (according to Mozilla docs).

Looks like many others aren't interested in easier solutions.