A few day ago, I received issue#15 Config mania option on Fx 4.0 new Menu button. I found Firefox 4.0b5 new menu is changed to 2-column.

<!-- Firefox 4.0b4 -->
 <menupopup id="appmenu-popup" ... >
   ...
 </menupopup>
<!-- Firefox 4.0b5 -->
 <menupopup id="appmenu-popup" ... >
   <hbox>
     <vbox id="appmenuPrimaryPane">
       ...
     </vbox>
     <vbox id="appmenuSecondaryPane">
       ...
     </vbox>
   </hbox>
 </menupopup>

Configuration Mania 1.12.2010082901 append "Configuration Mania" menu item is append on "appmenu-popup". On Firefox 4.0b5, it does not work well:

For Firefox 4.0b5 2-column menu, menuitem shall be append to "appmenuPrimaryPane", "appmenuSecondaryPane", or their submenus.

I moved "Configuration Mania" menuitem to Option submenu: