//Define o tipo de browser
  var browserType = null;
  if (navigator.userAgent.indexOf("Opera")!=-1 && document.getElementById)
    browserType = "OP"; //Opera
  if (document.all)
    browserType = "IE"; //Precisa explicar?
  if (document.layers)
    browserType = "NN"; //Netscape Navigator
  if (!document.all && document.getElementById)
    browserType = "MO"; //Mozilla