Thanks for the responses. I'll try to determine if the playback issue happens at particular points in particular videos.

The Youtube plugin seems to work quite well so far, by the way. One little quirk I've noticed, if I have a queue of youtube videos (which is a great feature!) and I'm viewing them in fullscreen, when the queue switches to the next video it pops out of fullscreen. If you're watching a longer video that has been divided into parts, that can be a little distracting.