I just wanted to add my voice. I had the same problem a while ago, and it just happened again. WindowBlinds was trying to update, but I ended up having to completely uninstall it. I am not sure I will reinstall. This is a serious bug.
I have had this happen to me twice on Firefox upgrades. I open up the newly upgraded FF, and for some reason, the titlebar is not skinned, and sometimes does not want to appear unless I minimize it and bring it back up again. Each time I had to figure it out for myself. If the titlebar is showing, but not skinned, double click on it. You may have to double click on it again to bring back the window, but now, it