title: Add submenu in menupopup mozilla extension developmet?
body: <p>Here I am working with firefox extension development. I have using <strong>XUL Overlays</strong>  to add menu popup item in my extension.</p>
  
  <pre><code>          &lt;menupopup id="menu_ToolsPopup"&gt; 
               &lt;menuitem label="HP Scheduler Options..."
                         insertafter="devToolsSeparator" 
                         oncommand="openPreferences('hpschedPane');" /&gt;
             &lt;/menupopup&gt; 
  </code></pre>
  
  <p>Here I need to add sub menu with menu item.</p>