The Tor Browser / file revision

 <?xml version="1.0"?>

 <window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"

         xmlns:html="http://www.w3.org/1999/xhtml"

         onload="run()">

     <tree id="tr" flex="1">

         <treecols>

             <treecol/>

         </treecols>

         <treechildren>

             <html:optgroup id="group">

                 <html:option id="victim" label="never see this"/>

             </html:optgroup>

         </treechildren>

     </tree>

     <script type="text/javascript"><![CDATA[

     function run() {

         group = document.getElementById("group");

         tc = document.createElement("treechildren");

         group.appendChild(tc);

         v = document.getElementById("victim");

         v.parentNode.removeChild(v);

         v = null;

         tree = document.getElementById("tr");

         col = tree.columns[0];

         alert(tree.view.getItemAtIndex(1, col)); 

     }

     ]]></script>

 </window>