title: XMLHttpRequest upload progress event doesn't work in Firefox 10.0.2
body: <p>I'm trying to create an ajax based upload form with progress bar. This is my code (the upload part of it):</p>
  
  <pre><code>$xhr = new XMLHttpRequest();
              $xhr.upload.addEventListener("progress",
                  function(e) {
                      if (e.lengthComputable) {
                          $progress = (e.loaded / e.total) * 100;
                          $('#file-progress').css('width', $progressWidth * (e.loaded / e.total));
                          $('#percentage').html($progress.toFixed(2) + '%');
                      } else {
                          alert('Y U NO WORK?');
                      }
                  }
              , false); 
  
  
              $xhr.onreadystatechange = function(e){
                  if($xhr.readyState == 4) {
                      //i'll add this later
                  }
              };
  
              $xhr.open('POST', 'handler.php', true);
              var $data = new FormData();
              $data.append('file', $file.files[0]);
              $xhr.send($data);
  </code></pre>
  
  <p>Everything works in Chrome (the progress bar and file upload) but in Firefox works only file upload without the progress bar. No errors, nothing. Firefox ignores the progress listener and i can't get why because as i have read Firefox should support XMLHttpRequest level 2.</p>