var n = document.getElementById("cfirma");
var cancho=720;
var calto=450;
if (navigator.appName=="Netscape" || navigator.appName=="Opera")
{
  var palto=window.innerHeight;
} else {
  var palto=document.body.clientHeight;
}
var ftop = palto - 32;
n.style["top"] = ftop;