I've noticed that file uploading isn't working properly on Windows 7 + Firefox. There are two issues I and one of our members have faced - File uploads 100% using flash uploader and then browser throws an error "There was problem uploading your attachment". Regular uploader (non-flash) opens, allows selection of file but the upload fails. Can you all check this with your websites? I'm running latest Xenforo. Note that this is FF+Windows issue. Works well on Mac (Chrome, FF, Safari) and Windows (Chrome).