Your problem is likely with Quicktime. This overzealous program tries to associate file types with itself that it really shouldn't. You need to go into your Quicktime preferences and disassociate it from being the default player for video files. Doing this fixed many video problems I was experiencing with my browsers.

If you have Apple update, you will need to fix this problem every time it automatically updates Quicktime, which is quite often. It is really annoying that Apple does this, apparently they think Quicktime is more important than any other player.