AnyColor

AnyColor is a Mozilla Firefox add-on designed to give your browser a new look by using new colors, transparency effects, and much more.

Just install the tool and restart Firefox to start changing your browser's appearance with any of the included preset themes.

There are dozens of new themes available. You can do anything from simply changing the background color to placing artistic images in the background, which (using transparency effects) can be seen behind the menu and navigation bars.

The program also lets you add effects to the tabs, use transparent layers, and even search for new themes if you don't like the ones that come with the program.