It's good that you mentioned it, but it should be said that the experience is far from perfect (at least in FF). Playback speed resets at every question break, each new video, etc. Audio drops out of sync frequently and seems to have more issues when sped up than in VLC.

I'm more comfortable downloading the lectures, but there are a few upsides to using their HTML5 player:

- When I speed up the video in VLC the pitch of the sound goes up. This doesn't happen for me in Chrome.

- You don't get the "in-video quizzes" when you download the lectures. Some courses put them up for download separately, for others there is no other way to get to them but through the online player. The quizzes don't typically (never?) count towards your final grade, but they can reinforce concepts and correct mistaken understanding early.

On the other hand,

- I have finer speed control in VLC, and

- The video players on my computer are just "nicer" than the web alternative, maybe better than a web alternative can be.