Firefox can expand to fill your entire screen with its Full Screen feature. It's great for those itty bitty screens on netbooks, making the most of your HDTV or just because you want it to! This article tells all you need to know about it.
Bigger is better! Fill up your whole screen with Firefox.
Gimme my computer back! Shrink Firefox back to it's original size.
For those with a good memory. Go Full Screen via the keyboard.