You must have a BlockBuster.com account and be logged in to be presented with the movie rating controls. It is free to create an account. Once you're presented with the ability to rate the movies by clicking on the 5 blue stars next to each movie, choose a rating and click on it. The blue stars turn into a indeterminate timebar. After several seconds, an error message pops up: Error Rating Failed This works in FireFox.
Checked the problem with Webkit r30153. The rating works for me as in Firefox.