così funziona ugualmente con IE7 e Firefox. A che serva non so , ma per andare, va :master:

codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>

</head>
<body>
    <input id="Button1" type="button" value="button" />
</body>
</html>

<script language="javascript" type="text/javascript">
// <!CDATA[
function funz1()
{
    document.getElementById('Button1').onclick = funz2;
}

function funz2()
{
    document.getElementById('Button1').onclick = funz3;
}

function funz3()
{
    alert('ciao');
}

funz1();

// ]]>
</script>