title: Firefox: Cross-domain requests with credentials return empty
body: <p>Firefox <a href="https://stackoverflow.com/questions/2054316/jquery-sending-credentials-with-cross-domain-posts">send a cross-domain post with credentials</a>, I can (using Charles - a proxy for HTTP debugging) see that the server is sending back the response… But Firefox isn't "letting me see it" (for lack of a better description).</p>
  
  <p>For example, using <a href="https://developer.mozilla.org/en/HTTP_access_control#Requests_with_credentials" rel="nofollow noreferrer">the documented example</a>:</p>
  
  <pre>
  >>> var invocation = new XMLHttpRequest();
  >>> invocation.open('GET', 'http://localhost/~wolever/cookie.php', true);
  >>> invocation.withCredentials=true;
  >>> invocation.onreadystatechange = console.log;
  >>> invocation.send()
  <a href="http://img.skitch.com/20100113-bq3a4qb1ufn52331x18ce3c7xu.png" rel="nofollow noreferrer">http://img.skitch.com/20100113-bq3a4qb1ufn52331x18ce3c7xu.png</a>
  >>> invocation.responseText
  ""
  >>> invocation.responseXML
  null
  </pre>
  
  <p>However, Charles tells me that this request has, in fact, returned the expected response:</p>
  
  <p><a href="http://img.skitch.com/20100113-njakyu4xequ5e3cyfhfnyeatq5.png" rel="nofollow noreferrer">http://img.skitch.com/20100113-njakyu4xequ5e3cyfhfnyeatq5.png</a></p>
  
  <p>Any idea what could be going wrong?</p>
  
  <p>And, incase it helps: the same request without credentials returns data as it should.</p>