Fullscreen Firefox?

I would like to make my Firefox fullscreen (without the Mac Taskbar on top), but I can find a viable solution. When researching a few places, I found out that there is an bundle called "Megazoomer" and it requires Simbl. Once I run the installer of Simbl and dragged the Megazoomer into my Library/Application Support folder. It doesn't work. It just makes a sfx noise that nothing is working.

When I press cmd + enter, it won't work. I don't know what I am doing wrong. Please let me know.

I am running Leopard on a 2.33 Ghz MacBook Pro. Thanks!