scontrol - cross browser - xml parser...

I am trying to create an scontrol that works in Mozilla (it already works in IE). The issue is with XML parsing. The IE version contains the following (create a doc, load, ans set properties):

xmlDoc = new ActiveXObject("Msxml2.DOMDocument.3.0");
xmlDoc.loadXML(msxml.responseText);
xmlDoc.setProperty("SelectionNamespaces", "xmlns:sf='urn:sobject.enterprise.soap.sforce.com'");
xmlDoc.setProperty("SelectionLanguage", "XPath");
var objNodeList = xmlDoc.documentElement.selectNodes("//sf:TotalPrice");

In Mozilla, I've gotten as far as creating and loading the doc. But where do I go from there? What API am I using to get at the elements? (Or is there a better way?)

xmlDoc=document.implementation.createDocument("urn:sobject.enterprise.soap.sforce.com","",null);
xmlDoc.load(msxml.responseText);

thanks
chris