The gtoolbar.xml is an xbl widget that includes <toolbox/> <toolbar/> and <menubar/> and provides an area, a button, to the toolbar and menubar for a graphic and tooltip. When a menubar or toolbar is wrapped in a <toolbox/> the  collapsable to icon/expand from icon functionality is enabled. The <toolbox/> has a tray area that holds any collapsed toolbars or menubars. The <toolbox/> can also contain other xul elements. The styling of the toolbox, toolbar, menubar is done in the toolbar.css or bound to any stylesheet you choose. <toolbox/>, toolbar/>, <menubar/> may be manipulated through the dom also.

USAGE:
The collapse/expand functionality is achived by wrapping a toolbar or menubar in the toolbox tag:
	<toolbox>
	  <toolbar>
	   <menubar/>
	  </toolbar>
	</toolbox>
If no collapse functionality is desired then wrap your toolbars and menubars in in an vbox or hbox:
	<vbox>
	  <toolbar>
	   <menubar/>
	  </toolbar>
	</vbox>

Here is a definition that shows a non-collapsable menubar and a collapsable toolbar with tooltips for collapsed and expanded states:
	<toolbox>
          <menubar UPgrippytooltiptext="Expanded menubar"
	     grippytooltiptext="Collapsed menubar" Collapsable="false" />
	  <toolbar UPgrippytooltiptext="Expanded toolbar"
	     grippytooltiptext="Collapsed toolbar" Collapsable="true" />
	</toolbox>
Notice in the above toolbar definition the Collapsable parameter. This may be used in a toolbar or menubar when they are grouped together in a toolbox and some are collapsable and some are not.