function resizeIframe(){
  var ifr = document.getElementById("main");
  var ifrBody = ifr.contentWindow.document[getDocBody(ifr.contentWindow)];
  ifr.style.height=ifrBody.scrollHeight+"px";
}

function getDocBody(win){
  if (!win) win=window;
  if (win.document.compatMode && win.document.compatMode != 'BackCompat') { //standards compliant mode 
    return "documentElement";
  }
  return "body";
}