Help altering Firefox Theme

I have always used themes on my firefox to make it better.
I am currently using a downloaded theme that is almost perfect, but I want to alter the one thing i don't like about it. The problem is I can't find the files on my computer, Where are the themes stored?

Is it possible to alter an already downloaded theme (not the default but one downloaded and installed)? If so how do I do it so I can alter this thing.

 

On XP Start>Run>type in %appdata%
Go into Mozilla folder>FireFox>Profiles>Default.xxxx>Extensions One of those folders contains your theme. When you find the right folder then go into chrome and unzip[tugzip will do it] the .jar file. You will get a folder with all the elements of the theme. From there I guess you could google "edit FF theme".

Here's one that might get you started.

Good Luck!