FireFox warning "Unknown pseudo-class or pseudo-element 'hidden' " keeps running over and over
<p>I recently have discovered a warning happening in Firefox that says</p>

<blockquote>
  <p><strong>Warning:</strong> Unknown pseudo-class or pseudo-element 'hidden'</p>
</blockquote>

<p>Here is page <a href="http://eleven23.net/eleven23/beta/work/web/lounge22.php" rel="nofollow">http://eleven23.net/eleven23/beta/work/web/lounge22.php</a></p>

<p>And the warning happens when it gets to the part of javascript that has img:hidden</p>

<blockquote>
  <p>$('img:hidden').eq(0).fadeIn(500);//fades in the hidden images one by one
        i++;//add 1 to the count</p>
</blockquote>

<p>So Im wondering if anyone has an idea on how to resolve this warning. </p>

<p>Thanks!</p>
