window.onload = setup;

function setup() {
  if(document && document.getElementsByTagName){
    // do stuff here.
  }
}

myUserAgent = navigator.userAgent.toLowerCase();
var moz = !(myUserAgent.indexOf('compatible')>0); // includes ns3, ns4, ns6, cam & mfb.
if (moz) {
  document.write('<style type="text/css">');
  document.write('<!--');
  document.write('html {  height: 100%;  }');
  document.write('-->');
  document.write('</style>');
}