Also, in looking at the raw HTML, I see that you're triggering the jQuery Easing code before jQuery itself is even loaded.
And then you're loading TWO versions of jQuery on the same page!

Code:
<script type="text/javascript" src="includes/templates/sheffield_blue/jscript/jscript_xjquery.easing.1.3.js"></script>
<script type="text/javascript" src="includes/modules/pages/product_info/jscript_textarea_counter.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.2/jquery.min.js"  type="text/javascript"></script>
<script src="/jquery.easing.1.3.js"  type="text/javascript"></script>


<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" src="includes/templates/sheffield_blue/jscript/jquery-1.4.4.min.js"></script>