<treerow xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul" class="zebra">
<script xmlns="http://www.w3.org/1999/xhtml"><![CDATA[
function doe(){
  document.getElementById('b').parentNode.removeChild(document.getElementById('b'));
  document.getElementById('c').parentNode.removeChild(document.getElementById('c'));
}

setTimeout(doe, 200);
]]></script>

<box id="a"/>
<mtr xmlns="http://www.w3.org/1998/Math/MathML">
<box xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul" class="zebra" id="c"/>
</mtr>
<box style="display: inline;" id="b"/>

<style xmlns="http://www.w3.org/1999/xhtml">
#a { counter-reset: chicken 11 egg; }
#b { counter-increment: chicken -1 egg; }
*[class=zebra] { counter-increment: chicken 5; }
</style>
</treerow>