Today i stumbled upon personas, a Firefox extension that provides background images for the symbol and status bars. So you can use skins to have some more eye candy. Here's a little screenshot to get an impression of the look of it.
Once you've installed it - there are 3 steps left to do.
1. Type "about:config" in the address bar und assure that you'll be careful to Firefox
2. Type "personas" in the filter field beneath the address bar
3. Set theese 3 Options as follows
extensions.personas.authorizedHosts : sm-personas01.mozilla.org
extensions.personas.siteURL : http://sm-personas01.mozilla.org/store/
extensions.personas.url : http://sm-personas01.mozilla.org/store/
Now you can click on the little fox symbol in your status bar the choose a skin.
Update: New versions of will work properly and don't need the steps mentioned above.