Why firefox 10.1 uses full screen on Snow Leopard while Chrome and Safari do not?
Solution 1:
I love Divvy - it's something that I feel OSX needs and that would allow you to set a shortcut for it. Otherwise the green orb on the top left will take you to full height, and then you can drag out horizontally to your chosen width.
Alternatively, should you upgrade to Lion, Chrome has a full-screen mode which hides all the other apps.
Solution 2:
Mac OS X doesn't resize windows like Windows when maximized. Logically, having a browser window take up an entire screen is very verrrrryyy inefficient, since you end up with the two blank spaces on both sides. OS X makes a window big enough to show the content, but no bigger as to prevent wasting of screen space.
You can of course look for utilities to restore a more windows familiar feel - some I am aware of are moom, cinch, and divvy. A tutorial on using RightZoom may help as well.