title: $(":focus") returns no element for <input type="file" /> in Firefox
body: <p>I can't seem to get the currently focused/active element as a jQuery object <em>in Firefox</em>, if it is an <code>&lt;input type="file" /&gt;</code>. It works on other input types (text, password, submit, others) and on other element types (<code>&lt;select&gt;</code>, <code>&lt;textarea&gt;</code>, others).</p>
  
  <h2>HTML</h2>
  
  <pre class="lang-html prettyprint-override"><code>&lt;input type="file" /&gt;
  </code></pre>
  
  <h2>Javascript</h2>
  
  <pre class="lang-js prettyprint-override"><code>// Cannot find input type file elements with :focus,
  // $focused.length is always 0 in Firefox (tested using FF 10.0.1)
  var $focusedTest1 = $(':focus');
  
  // This line throws for Firefox (tested using FF 10.0.1)
  // Permission denied to access property 'nodeType'
  // @ http://code.jquery.com/jquery-1.7.1.js:108
  // in jQuery.fn.init, below "Handle $(DOMElement)"
  var $focusedTest2 = $(document.activeElement);
  </code></pre>
  
  <h2>Steps to reproduce</h2>
  
  <ol>
  <li>Use Firefox.</li>
  <li>Focus the file box:
  <ul>
  <li>press tab until you reach it</li>
  <li>or click in it.</li>
  </ul></li>
  <li>While focusing the file box, try to get a result from <code>$(':focus')</code>.</li>
  </ol>
  
  <p>See <a href="http://jsfiddle.net/joelpurra/bzsv7/" rel="nofollow">jsFiddle demonstration of getting the id of the focused element</a> - test it with Firefox.</p>
  
  <p><strong>Does anyone have a solution for getting the focused/active element as a jQuery object that works for <code>&lt;input type="file" /&gt;</code>?</strong></p>
  
  <p>The solution needs to be fully generic as the functionality is part of a plugin. I will not have control over the page the script will run on.</p>