I haven't looked into it but I strongly suspect that the problem is within the "moveIt" method.
It uses "event", which unless it is a property of window (i.e. window.event) it is not in scope.
I believe in IE, window.event is defined, whereas in all other normal browsers () it is not. Instead the event is passed to the listener. Therefore, to get that script to work moveIt should take event as a parameter (and may also have to use different properties of it, I can't remember exactly...)