<?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.remove();
        v = null;

        tree = document.getElementById("tr");
        col = tree.columns[0];
        alert(tree.view.getItemAtIndex(1, col)); 
    }
    ]]></script>
</window>