title: Missing click event for <span> inside <button> element on firefox
body: <p>I am experiencing problem with Firefox 32 when I bind action on click event of span element inside a button element. Other browsers seems to works well.</p>
  
  <p>Here the <a href="http://jsfiddle.net/tqf0z7x5/" rel="noreferrer">code illustrating the issue on jsFiddle</a>.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;span onClick="alert('test');"&gt;**Working**&lt;/span&gt;&lt;br&gt;
  &lt;button&gt;inside a button &lt;span onClick="alert('test');"&gt;**Not working**&lt;/span&gt;&lt;/button&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>Does anybody know why and if it's a bug or a feature ?</p>