Hey, I just got an update to the Firefox Personas plugin (version 1.6.1) and Customize Persona finally works.
Now I can get busy creating some nice personas for myself and get rid of the ugly Win7 blues, in Firefox anyway. I wish I could do that in all my programs.
My Persona in the above screenshot is just a simple diagonal yellow and green gradient I used for testing purposes. Nothing fancy, but I like it. You can see my nice Windows 7 Purple window theme too.
Personas blogged previously here.