Unable to parse XmlDocument in Firefox

 Dear Friends,
I am getting a XMLDocument from a webservice after calling it from a JS function. In the Callback function I am trying to parse the XMLDocument  but I am getting the error "xmlDoc.documentElement is null"
The code is as below:
 function SucceededCallback(result, eventArgs) {
//check if it is NON-MS browser

  if (window.XMLHttpRequest) {
 
          var xmlDoc = document.implementation.createDocument("", "", null);
          alert(xmlDoc);
          xmlDoc.load(result);
          xmlDoc.onload = function() {
          alert("XML Root Tag Name: " + xmlDoc.documentElement.tagName);
     &n ...