With the combination of elements menu menupopup, and menuitem arbitrary menubars can be created.

A simple example

The elements can be nested to create a hiearchic menu.

<?xml-stylesheet href="css1.css" type="text/css"?>
<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
align="vertical" >
     <menubar>
          <menu value="AAA">
               <menupopup>
                    <menu value="aaa">
                         <menupopup>
                              <menuitem value="a X1"/>
                              <menuitem value="a X2"/>
                         </menupopup>
                    </menu>
                    <menu value="bbb">
                         <menupopup>
                              <menu value="b Y1">
                                   <menupopup>
                                        <menuitem value="One"/>
                                        <menuitem value="Two"/>
                                   </menupopup>
                              </menu>
                              <menuitem value="b Y2"/>
                         </menupopup>
                    </menu>
               </menupopup>
          </menu>
          <menu value="BBB">
               <menupopup>
                    <menuitem value="111"/>
                    <menuitem value="222"/>
               </menupopup>
          </menu>
     </menubar>
</window>

xul3.xul

With the element menuseparator groups of items can be separated

css1.css

The default Mozilla CSS is used.

@import url(chrome://global/skin);