Пример кода для первой страницы:

<html>
<head>

    <script language="Javascript">

        function showFBWindow(){
            url = "allowfbchild.html"
            newwindow=window.open(url,'name','height=200,width=150');
            if (window.focus) {newwindow.focus()}
        }

    </script>

</head>
<body>

    <input type="button" OnClick="showFBWindow()" value="Open FB" />

</body>
</html>

Пример кода для второй страницы:

<html>
<head>

    <script language="Javascript">

        function redirectToFB(){
            window.opener.location.href="http://wwww.facebook.com";
            self.close();
        }

    </script>

</head>
<body>

    Allow the user to view FB
    <br/>Are you sure?
    <input type="button" value="Ok" OnClick="redirectToFB()" />

</body>
</html>