I bet you’re using a Firefox theme right now. What I doubt is that you like the default Firefox look and I also doubt you’re using Personas For Firefox. Personas is a more lightweight and customizable solution to Firefox themes. You can customize the way Firefox looks without knowing all the codes! Plus it’s more elegant IMO. It’s extremely simple to use, all you have to do is click on the Personas symbol at the bottom-left corner and choose your skin! Although sometimes the Persona “un-loads” and you’re left with a horrible blank Persona, since the Persona’s are not on your computer; they’re on a web server.
Here’s what mine looks like:
As you can see, I have Firefox Personas installed. I'm using the Firefox Logo persona.