title: Select2 v4 unable to tab into, press enter, and then select, with Firefox (aka mouseless access)
body: <p>I am currently unable to tab into a Select2 enabled <code>&lt;select&gt;</code> element in Firefox (38.0.5) - in other words, cannot access to select <code>&lt;option&gt;</code> in a mouseless manner. In Chrome, you can tab through a form and press <kbd>enter</kbd> in order to start selecting an item in the Select2 <code>select</code> element. I have not tested in other browsers, but before submitting an actual bug report I want to verify whether others are experiencing the same issue?</p>
  
  <p>You can <a href="https://select2.github.io/examples.html" rel="noreferrer">duplicate on the demo page</a>.</p>
  
  <ul>
  <li>Select2 v4.0.0 </li>
  <li>Twitter Bootstrap 3.3.4 (although have not added any
  additional items to style for Bootstrap) </li>
  <li>Firefox v38.0.5</li>
  </ul>