function detectMacXFF() {

  var userAgent = navigator.userAgent.toLowerCase();

  if (userAgent.indexOf('mac') != -1 && userAgent.indexOf('firefox')!=-1) {

    return true;

  }

}

  var d = detectMacXFF(); //note new detectMacXFF2 script above

  if (d) {

  document.write("<style>.Mission h1 {font-size:23px;letter-spacing:.035em;}</style>");

 }