title: document.getElementById does not work on Firefox
body: <p>Firefox returns null when I try to call document.getElementById on an element.</p>
  
  <p>Here is the call </p>
  
  <pre><code>document.getElementById('interaction4793')
  </code></pre>
  
  <p>However the element is present in the DOM. I can find it</p>
  
  <pre><code>&lt;interaction id="interaction4793"&gt;
      &lt;action id="action3268" trigger="enter" type="hover" /&gt;
      &lt;reaction delay="0" id="reaction3709" options="reloadOnly" target="page0001" transition="none" type="showPage" /&gt;
  &lt;/interaction&gt;
  </code></pre>
  
  <p>Even when I select it from the inspector and use the <a href="https://developer.mozilla.org/en-US/docs/Tools/Page_Inspector" rel="nofollow">$0</a> trick it returns null:</p>
  
  <pre><code>document.getElementById($0.id)
  </code></pre>
  
  <p>When I try to get the elements from getElementsById it works.</p>
  
  <p>EDIT:
  Chrome and Safari do not return null. I tested Firefox (version 26) on Window and MacOS both return null.</p>
  
  <p>EDIT2:
  I think Firefox do not understand that the attribute <code>id</code> is the id. When I search by attribute with jquery I can find the interaction:</p>
  
  <pre><code>console.log($('#interaction102').length); // returns 0
  console.log($('[id="interaction102"]').length); // returns 1
  </code></pre>