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

tooltip {
  -moz-appearance: none !important;
  font: message-box !important;
  color: #ffffff !important;
  background-color: transparent !important;
  background-image: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAABmJLR0QA/wD/AP+gvaeTAAAAGElEQVR42mNkYGCoZyACMDEQCUYVUkchANsIAJN3G7QXAAAAAElFTkSuQmCC") !important; 
  border: 1px solid #000000 !important;
}