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

#appmenu-toolbar-button > .toolbarbutton-menu-dropmarker, 
#appmenu-toolbar-button > .toolbarbutton-text {
      display: none !important;
    }

#appmenu-toolbar-button { 
list-style-image: url("chrome://branding/content/icon16.png") !important;
}