/* The following CSS code will hide menubar
and show them again if you move the cursor to menubar */

/* begin css */

@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

#toolbar-menubar{
  visibility: collapse !important;
}

#navigator-toolbox:hover > #toolbar-menubar{
  visibility: visible !important;
}

/* end css */