Possible Duplicate:
Screensaver suppression on video playback
How do I stop the screensaver from turning on when I watching online videos?
I have managed to stop screen saver with vlc. But it seems that when I am watching a movie on firefox the screen saver pops in again, in a few mins. How can I tell my ubuntu 12.04 that I am watching a movie in firefox and not to turn on the screen saver each time I do so?