Creating a DOM Document from HTTP Request of XML failing

Hi,

I send an HTTP Request, which returns the following XML.

<?xml version="1.0" encoding="UTF-8"?>
<users_getInfo_response xmlns="http://api.facebook.com/1.0/"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://api.facebook.com/1.0/
http://api.facebook.com/1.0/facebook.xsd" list="true">
  <user>
    <about_me xsi:nil="true"/>
    <first_name>Chewy</first_name>
    <last_name>Cat</last_name>
    <uid>100000495237103</uid>
    <pic_square>http://profile.ak.fbcdn.net/v22944/850/83/q10000049523710
3_4003.jpg</pic_square>
  </user>
</users_getInfo_response>


To parse the XML, my understanding is I should create a document. (Is
such correct?)
So to create a DOMDocument, I have the following C++ code:

nsCOMPtr<nsIDOMDocument> document;
rv = inXMLHttpRequest->GetResponseXML(getter_AddRefs(document));
NS_ENSURE_SUCCESS(rv, rv);
NS_ENSURE_TRUE(document, NS_ERROR_FAILURE);
  <rest of my code>

rv does not get an error. eg rv is set to NS_OK, but the raw pointer
of document, ends up being null, and the NS_ENSURE_TRUE exits my
routine, so the <rest of my code> does not execute.

Why is this happening? Is my XML not proper?   Any thoughts?

Thanks in advance,

-cris