title: dragenter, dragover and drop events not working in firefox
body: <p>I have the following code in my js file</p>
  
  <pre><code>window.onload = function () {
  
      var canvas = document.getElementById('canvas');
      canvas.addEventListener('dragover', drag_over, false);
      canvas.addEventListener('dragenter', drag_over, false);
      canvas.addEventListener('drop', dropped, false);
  }
  </code></pre>
  
  <p>And at some point I create a draggable element like this</p>
  
  <pre><code>element.addEventListener('dragstart', dragstart, false);
  </code></pre>
  
  <p>I have callbacks like this:</p>
  
  <pre><code>function dragstart(e) {
      console.log("dragstart");
  }
  
  function dropped(e) {
      console.log("dropped");
   }
  function drag_over(e) {
      console.log("dragover");
      e.preventDefault();
      return false;
  }
  </code></pre>
  
  <p>The problem is that the code works fine in chrome but not in firefox.
  In firefox, dragstart callback gets fired but not the rest of them. Clueless :(</p>