Full Screen Pop-up HTML Window

I really hate for my 4th post to be another help me out post but… I wish to make it so that when you click the enter button on my site it launches full screen. Like this site www.liquidgeneration.com

I used the tutorial on this site and searched to forums. But the tutorial doesnt work in firefox. And I cant find what I need in the forums. I am really bad with HTML. Also how could I make it detect the window size so that it launches full screen on every computer.