We all want more attention to be played to the active tab inside of Firefox, that seems to be one thing that is asked for over and over again. Well, as with many problems you might face, Firefox has more than one solution to be had.
The Hard Way – Editing Your userChrome.css
They have a pretty good write up on how to do this over at Mozilla Links that you should check out if you are interested in doing it this way. I have heard some people having issues with this fix though. It worked fine for me, but just in case let me give you an alternative.
The Easy Way – Install the Aging Tabs Extension
Out of all the coloring and highlighting tab extensions out there, I love Aging Tabs the most. Firefox is open a long time on my PC and over time I want to see some tabs more than others. This extension allows you to customize the color of your active tab and the surrounding tabs as well.