<xul xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul" onload="boom();"> <script type="text/javascript"> function boom() { var XUL_NS = "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"; var oldListbox = document.getElementById("oldListbox"); var listitem = document.getElementById("listitem"); var newListbox = document.createElementNS(XUL_NS, "listbox"); var newHbox = document.createElementNS(XUL_NS, "hbox"); oldListbox.appendChild(newListbox); listitem.appendChild(newHbox); newListbox.style.display = "inline"; oldListbox.style.display = "block"; newHbox.style.display = "inline"; } </script> <listbox id="oldListbox"><listitem id="listitem" /></listbox> </xul>