Color Tabs Yourself Rated 4 out of 5 stars
Check out the following two links which will show you how to change the color of tabs yourself in any version of FF.
I have mine set to a blue background with white text for unfocused tabs and a yellow tab with black text for the focused tab. All you need to modify is the RGB color codes in the example. I did a google search for "RGB color codes" to get the ones I wanted.
Colorful Tabs 3.1 is very nice as eye candy but may be a little too much for some users.