//detecta navegador
    function checkIt(string){
         var detect = navigator.userAgent.toLowerCase();
         place = detect.indexOf(string) + 1;
         thestring = string;
         return place;
    }

    //adaptar la altura del iframe a su contenido
    function resize() {
         if (checkIt('opera')){
         alert("opera")
          document.getElementById("myframe").height =
        document.getElementById("myframe").document.body.scrollHeight;
         }
         document.getElementById("myframe").height =
        document.getElementById("myframe").contentWindow.document.body.scrollHeight;
    }