I hear 1.25x is fairly optimal for watching MOOC videos so I opted into the Youtube HTML 5 beta according to the provided instructions to get faster than 1x video playback. That's nice, I didn't know Youtube had an HTML 5 test going on. Flash sucks.
Turns out Youtube doesn't offer 1.25, just 1.5. And turns out I only get the HTML 5 version by clicking the "Watch on Youtube" link in the MOOC, rather than seeing it in the MOOC. Neither is ideal but I'll see how it goes.