Good for increasing the speed of YouTube videos beyond YouTube's own limit of 2x.

Partly works on YouTube in Firefox Nightly for Android. Controller indicator works in desktop view. In mobile view, it doesn't respond to touch, disappears after a couple of seconds, and can't be brought back with a tap. Switching to desktop view is a reasonable workaround, but fix the mobile-view issues and you'll have a complete winner.

YouTube High Definition has to be disabled for the "force last speed" function to work. No worries about that, but just an observation for anyone puzzled by the function not working.