Thank you Steven for your reply.
I had been experimenting a bit myself and found that this works:

<div id="pagecontent" name="pagecontent" style="visibility:hidden;display:none;padding-left:10px;padding-right:10px;">
    <script src="/jbcore/juicebox.js"></script>
    <script>
        new juicebox({
            containerId : 'juicebox-container',
            configUrl : '/fotografie/LarryCarlton/131104/jbfotos.xml',
            galleryWidth : '100%',
        });
    </script>
    <div id="juicebox-container"></div>
</div id="pagecontent">
<script type="text/javascript">
  $(document).ready(function(){
    $('#pagecontent').css('display', 'block');
    $('#pagecontent').css('visibility', 'visible');
  });
</script>

Why this "delayed display" works, beats me. But it does.

Yep, works! Thanks!