Firefox now has an addon that allows a boat load of new themes for the browser's look. Once you download and the browser restarts the place to click is the lower left corner. You can go to the themes and just put the mouse over them and they will give a preview to look at before you choose to make it your choice.
https://addons.mozilla.org/en-US/firefox/addon/10900
https://addons.mozilla.org/en-US/firefox/addon/10900
