if (navigator.userAgent.indexOf('WebKit')>-1) {
  document.write('<link rel=\"stylesheet\" type=\"text/css\" media=\"screen\" href=\"/styles/default.safari.screen.css\" />');
}
if ((navigator.userAgent.indexOf('Firefox')>-1)&&(navigator.userAgent.indexOf('Mac')>-1)) {
  document.write('<link rel=\"stylesheet\" type=\"text/css\" media=\"screen\" href=\"/styles/default.ffmac.screen.css\" />');
}