The error also occurs in other web browsers too.
The error is that firstChild is trying to be applied to null, instead of an element.
It looks like gg() cannot get the firstChild property of the a variable. gg() is called by df(), which in turn is called by ew(), which is loaded as a part of the google maps protocol.
Here's the root cause of your trouble.
var map = new GMap2(document.getElementById("map"));
You have no element with a unique identifier of "map"