example1.xul

<?xml version="1.0"?>
<?xml-stylesheet href="chrome://global/skin/" type="text/css"?>
<window id="yourwindow" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">

<label value="Horizontal layout"/>
<hbox>
  <button label="horizontal1" flex="1"/>
  <button label="horizontal2" flex="2"/>
  <button label="horizontal3" flex="3"/>
</hbox>
<label value="Vertical layout"/>
<vbox>
  <button label="vertical1"/>
  <button label="vertical2"/>
</vbox>
<label value="mixed"/>
<hbox>
  <button label="mixed1" flex="3"/>
  <vbox flex="2">
    <button label="mixed2" />
    <button label="mixed3" />
    <button label="mixed4" />
  </vbox>
  <button label="mixed5" flex="1"/>
</hbox>


</window>