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

#rip-status-bar > .statusbarpanel-icon {
  width: 0 !important;
  padding-left: 16px !important;
  background-image: url(your image here) !important;
  background-repeat: no-repeat !important;
  background-position: center center !important;
}