Unfortunately selectSingleNode function doesn't works with Firefox/Chrome. This is primitive way IE used to handle the XML Parsing. 

I tried out an example with AJAX response. Hence the XMLHttpRequest responseXML object was successfully processed using selectSingleNode() for any of the tree element in the document object in IE. On the contrary it doesn't work with Firefox/Chrome.

To make it work across we will need to handle the response XML a little differently. We can use getElementsByTagName("<tagName>") to get an array of nodes and hence proceed further.

~Praveen