Firefox not playing videos

Generally I save videos to watch them but some sites insist on watching videos in a webpage. For some reason my firefox can't play them. It says its missing a plugin. When I click to download it it says it can't find one. So what plugin am I missing? It wont play any media in a window I don't think. I am using media player classic and real alternatives for quicktime and real.

Hey, credit where credit is due. The rendering engine in FF isn't shitty. Oh, if only IE had an engine like that!

Everything else is true though.