offsetHeight not working in Firefox

[bob2044]

offsetHeight is not working in following code

<script type="text/javascript">
function Coverdiv()
{
    var standard=(document.compatMode=="CSS1Compat") ? document.documentElement:document.body;
    var dv = document.createElement("div");
    dv.setAttribute("id","cover");
    document.body.appendChild(dv);
    var cover=document.getElementById("cover");
    //dv.innerHTML="Samit";
    cover.style.top=0+"%";
    cover.style.left=0+"%";
    cover.style.backgroundColor="#000000";
    cover.style.zIndex=100;
    cover.style.height=100+"%";
    cover.style.position="absolute";
 
    cover.style.width=100+"%";
    cover.style.height=document.body.offsetHeight;
    cover.style.opacity="0.8";
 
    var contDiv=document.createElement("div");
    contDiv.setAttribute("id","Contents");
    document.body.appendChild(contDiv);
    var Content=document.getElementById("Contents");
 
    Content.innerHTML="Samit";
    Content.style.top=50+"%";
    Content.style.left=50+"%";
    Content.style.backgroundColor="#FFFFFF";
    Content.style.zIndex=101;
    Content.style.height=20+"%";
    Content.style.width=20+"%"
    Content.style.position="absolute";
};
window.onload=Coverdiv;
</script>

[acoder]

What do you expect it to be and what is it instead? Perhaps you should be using the greater of scrollHeight/offsetHeight.