@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);
menuitem[command="cmd_newNavigator"], #menu_closeWindow, menuitem[id="placesContext_open:newwindow"], #context-openlink, #contentAreaContextMenu #frame menuitem[oncommand='gContextMenu.openFrame();'] {
  display: none !important;
}