让firefox支持children

<iframe marginwidth="0" marginheight="0" src="http://218.16.120.35:65001/PC/Global/images/b.html" frameborder="0" width="728" scrolling="no" height="90"></iframe>
HTMLElement.prototype.__defineGetter__("children",
function () {
var returnValue = new Object();
var number = 0;
for (var i=0; i<this.childNodes.length; i++) {
if (this.childNodes[i].nodeType == 1) {
returnValue[number] = this.childNodes[i];
number++;
}
}
returnValue.length = number;
return returnValue;
}
);