title: jQuery Ajax beforeSend does not works in Firefox
body: <p>I'm trying to execute an ajax-post request using jQuery, and I need to add custom headers (for dJango CSRF). I've tried some code like this:</p>
  
  <pre><code>var load = function() {
      $.ajax({
          type: 'POST',
          url: '/ajax/get_page/',
          data: $.toJSON({
              section: section,
              subsection: subsection,
              page: page.page
          }),
          beforeSend: function(xhr, settings) {
              xhr.setRequestHeader("exmpl", "abcdef");
          },
          success: function (data){
              container.html(data);
              page.init(container);
              show();
          }
      });
  }
  </code></pre>
  
  <p>And it works fine in Chrome, but doesn't work in Firefox (Fedora, Firefox 8, jQuery 1.7). It seems that it don't even execute beforeSend function.</p>
  
  <p>Any ideas?</p>