<?xml version="1.0"?>

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

<grid>
  <columns>
    <column id="col1" flex="1"/>
  <column id="col2" flex="1"/>
    <column id="col3" flex="P-2"/>
  </columns>
</grid>

</window>