Sometimes when I am running Firefox (and I think Safari) I get this hidden window. It is not found in the window menu. It is not selectable when I am in expose, when I click on it, it does not appear, but i am sent to Firefox (or safari). The only way I know it is there is when i am expose'ing. It is always the same size and in the same place on the screen. What do you think it is? I have attached a shot of it during expose and did a bad job of highlighting it.