Fullscreen fps very low

When I'm watching a video through Safari or Firefox (even tried Chrome and still doesn't work) and I go into fullscreen mode, the fps drops significantly. The original video plays smoothly no matter how high quality it is, but the fullscreen playback of that same video even at the lowest quality is horrible. Basically, I can see the video, but it consistently skips/lags.

Oddly enough, the playback is fine if I use the zoom feature (contol + two fingers), even though the computer's display has to manage the same resolution video with the zoomed video as the fullscreen video. This leads me to think that the issue might not be the mac's resolution or display.

I've also spent awhile working on the browsers/connection, such as updating the flash and fussing with the proxy settings, and still can't get this fixed, so it seems like it isn't the flash player or network. My roommate can watch fullscreen vids fine.

Any help would be greatly appreciated!