How to get Firefox window back to transparent?

Hey everybody, I've got an odd problem that I've been searching everywhere for. See, while I was laying in bed my cat walked across my laptop (I know, happens rite?). Anyway, she somehow turned my firefox window from transparent to opaque. The problem is, it's only the Firefox window, everything else is fine and still retains the theme I selected. Here, have a look for yourself (If I attached the screenshot correctly, that is). So now, I can't figure out what the hell she did. My cat must've hit the most obscure shortcut combination out there, because going through menus and options in both Firefox and 7 I haven't been able to find it, and even forums and how-to's have no information on the matter. I guess it just takes your cat to break things to force you learn more about how to fix it. Anyway, I just wondering if you've run into this before, and have any info on it.

Hallo Frank, if you try going into Tools>Add ons & change your Theme back to the default, restart firefox then reselect your custom theme or persona (by the look of your screenshot & how things have gone black i am picking you are using a persona?)

Hope this helps

my firefox turns opaque every time i watch some video on youtube. so it's flash related :/