I uploaded your jscript file to my test site. I get the same issue. When I added the closing tag for the popup image above it. It works.

Here my code: try it again and make sure it gets uploaded correctly and to the right folder... /includes/modules/pages/product_info/

Code:
<?php
//
// +----------------------------------------------------------------------+
// |zen-cart Open Source E-commerce                                       |
// +----------------------------------------------------------------------+
// | Copyright (c) 2003 The zen-cart developers                           |
// |                                                                      |
// | http://www.zen-cart.com/index.php                                    |
// |                                                                      |
// | Portions Copyright (c) 2003 osCommerce                               |
// +----------------------------------------------------------------------+
// | This source file is subject to version 2.0 of the GPL license,       |
// | that is bundled with this package in the file LICENSE, and is        |
// | available through the world-wide-web at the following url:           |
// | http://www.zen-cart.com/license/2_0.txt.                             |
// | If you did not receive a copy of the zen-cart license and are unable |
// | to obtain it through the world-wide-web, please send a note to       |
// | [email protected] so we can mail you a copy immediately.          |
// +----------------------------------------------------------------------+
// $Id: jscript_main.php 5444 2006-12-29 06:45:56Z drbyte $
//
?>
<script language="javascript" type="text/javascript"><!--
function popupWindow(url) {
  window.open(url,'popupWindow','toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=no,resizable=yes,copyhistory=no,width=100,height=100,screenX=150,screenY=150,top=150,left=150')
}
function popupWindowPrice(url) {
  window.open(url,'popupWindow','toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=yes,copyhistory=no,width=600,height=400,screenX=150,screenY=150,top=150,left=150')
}
//--></script>


<script type="text/javascript">
(function() {
    window.PinIt = window.PinIt || { loaded:false };
    if (window.PinIt.loaded) return;
    window.PinIt.loaded = true;
    function async_load(){
        var s = document.createElement("script");
        s.type = "text/javascript";
        s.async = true;
        if (window.location.protocol == "https:")
            s.src = "https://assets.pinterest.com/js/pinit.js";
        else
            s.src = "http://assets.pinterest.com/js/pinit.js";
        var x = document.getElementsByTagName("script")[0];
        x.parentNode.insertBefore(s, x);
    }
    if (window.attachEvent)
        window.attachEvent("onload", async_load);
    else
        window.addEventListener("load", async_load, false);
})();
</script>

<div id="fb-root"></div>
<script>(function(d, s, id) {
  var js, fjs = d.getElementsByTagName(s)[0];
  if (d.getElementById(id)) return;
  js = d.createElement(s); js.id = id;
  js.src = "//connect.facebook.net/en_US/all.js#xfbml=1&appId=123886947641592";
  fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>