[adimitrov]

Video player's hidden controls react to mouse movement in the screen area though, a web browser would need a different heuristic — like moving the mouse close to where the controls should be or somesuch.

There's people arguing, of course, that that's really poor usability, because you can't see what you can do. I guess it's a matter of taste as much as anything, and it's probably more of a power-user thing.)