Plugin schmugin. Try my bookmarklet:
javascript:void%20function(){document.querySelector(%22video%22).playbackRate=parseFloat(prompt(%22Set%20the%20playback%20rate%22))}();
Works on all HTML5 video that's not inside an iframe or otherwise inaccessible to the page-level DOM.
Only tested on FF for Windows and Linux, but it's just vanilla JS.
https://chrome.google.com/webstore/detail/video-speed-contro...