title: Post is not working properly on IE9
body: <p>I'm trying to post form and to receive server response in a target iframe using just plain HTML. What i have so far is:</p>
  
  <pre><code>&lt;iframe name="iframe" id="iframe" onload="loaded()" style="display:none"&gt;&lt;/iframe&gt; 
  </code></pre>
  
  <p>than i have:</p>
  
  <pre><code>&lt;form id="form" action="/rpc/test" method="post" target="iframe"&gt;
      &lt;!--....... form input ............--&gt;
      &lt;input type="submit" class="button" name="Test" id="Test" value="Test"&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>and finally in the script tag i have the function loaded which need to process the response:</p>
  
  <pre><code>&lt;script language="javascript" type="text/javascript"&gt;
  function loaded() {
      var ifr = document.getElementById('iframe');
      var dc = ifr.contentWindow || ifr.contentDocument;
      if (dc.document) {
          dc = dc.document;
      }
      var rsp = dc.documentElement.innerText || dc.documentElement.textContent;
      var obj = JSON.parse(rsp);
      if (obj &amp;&amp; obj.success === true) {
          // DO very important things
          return;
      }
  }
  &lt;/script&gt;
  </code></pre>
  
  <p>This works absolutely ok in every possible browser except IE9 (don't test it on lower IE versions though). In IE9 the response is a file which contains the correct server response. IE9 asks me "Do you want to open or save .....?" </p>
  
  <p>My server is nodejs. I set response:</p>
  
  <pre><code>resposnse.writeHead(200, { 'Content-Type': 'application/json' });
  </code></pre>
  
  <p>I can track in the IE9 network monitor that Content-Type is 'application/json'</p>
  
  <p>Any ideas?</p>