Firefox Msxml2.DOMDocument equivalently

Here is a verbose way that should work:
function TransformXmlWithXsl(xmlDocumentPath, xslDocumentPath){        
 var xsltProcessor = new XSLTProcessor();
// *** load the XSL file
var myXMLHTTPRequest = new XMLHttpRequest();
myXMLHTTPRequest.open("GET", xslDocumentPath, false);
myXMLHTTPRequest.send(null);
// *** get the XML document
xslStylesheet = myXMLHTTPRequest.responseXML;
 xsltProcessor.importStylesheet(xslStylesheet);
// *** load the xml file
myXMLHTTPRequest = new XMLHttpRequest();
myXMLHTTPRequest.open("GET", xmlDocumentPath, false);
myXMLHTTPRequest.send(null);
var xmlSource = myXMLHTTPRequest.responseXML;
// *** transform
return xsltProcessor.transformToFragment(xmlSource, document);
}

the XMLHTTPRequest's really aren't necessary, but I'm not sure what you're sending in.
Also, you might want the transformToDocument function instead of fragment, but again that's up to you.

// first part
var xmlDocument = new ActiveXObject("Msxml2.DOMDocument.4.0");
      xmlDocument.loadXML(xmlString);  


What about fisrt part I try DOmParser but there in no propert to see xmlstring in it.