The Tor Browser / file revision

 <?xml version="1.0"?>

 <?xml-stylesheet href="chrome://global/skin/" type="text/css"?>

 <window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul" onload="boom();">

 <hbox style="display: none;">

   <bindings xmlns="http://www.mozilla.org/xbl">

     <binding id="x">

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

     </binding>

   </bindings>

 </hbox>

 <script type="text/javascript">

 function boom()

 {

   document.getElementById("b").style.MozBinding = "url('#x')";

   // Flush layout.

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   document.getElementById("listbox").removeChild(document.getElementById("c"));

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 <listbox id="listbox"><listitem/><listitem id="b"/><listitem id="c"/></listbox>

 </window>