function resizeIframe(ifr){
//var ifr = document.getElementById("mainIframe");
var ifrBody = ifr.contentWindow.document[getDocBody(ifr.contentWindow)];

ifr.style.height=ifrBody.scrollHeight+"px";
ifr.style.width=ifrBody.scrollWidth+"px";
}

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