title: Firefox CORS Cross Domain Resource Sharing Pre-Flight Debugging
body: <p>I'm trying to get Firefox to allow me to make an XmlHttpRequest for data from an application port.</p>
  
  <p>I can see that the initial send triggers an OPTIONS message, and I have trapped this using NetMon, and I can see the HTTP fields...</p>
  
  <pre><code>OPTIONS /any.htm HTTP/1.1
  Host: www.mysite.co.uk:10090
  User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:18.0) Gecko/20100101 Firefox/18.0
  Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
  Accept-Language: en-gb,en;q=0.5
  Accept-Encoding: gzip, deflate
  DNT: 1
  Origin: http://www.mysite.co.uk
  Access-Control-Request-Method: POST
  Access-Control-Request-Headers: content-type
  Connection: keep-alive
  Pragma: no-cache  
  Cache-Control: no-cache
  </code></pre>
  
  <p>I respond to this with an OK to tell FireFox to get a move on and send me the data in the XHR request...</p>
  
  <pre><code>HTTP/1.1 200 OK
  Access-Control-Allow-Methods: POST,-GET,-OPTIONS
  Access-Control-Allow-Origin: *
  Access-Control-Max-Age: 172800000
  Server: Kawasu-OrderSub
  Date: Wed, 23 Jan 2013 15:00:50 GMT
  </code></pre>
  
  <p>But the POST is never sent, which I assume means that FireFox is not happy with the 200 OK response.  The POST sends data with a Content-Type of "application/json"</p>
  
  <p>I've got FireBug and the Net tab has the XHR button, but this will only show the XHR after the pre-flight check has been passed. </p>
  
  <p>Main Question: How can I see (and debug) what FireFox does not like about the server response?</p>
  
  <p>Much obliged for any help in advance.</p>