Update to the original post: None of the suggestions here and elsewhere (inlcuding Symantec's own info) have worked.

Unless I completely disable NIS (not just Ad Blocking), the page is not displayed properly.

2nd Update: Today it works! I'm not sure if my NIS was updated (I share this machine with the household, and they're all asleep now), or if something changed on PM that affected it.

Here's the old html that didn't work:

<script type="text/javascript"></script>
    function toggleMenu(id){
      element = document.getElementById(id);
      element.className = (element.className.toLowerCase() ==
                            'expanded' ? 'collapsed' : 'expanded');
    }
[download]

and here's the new that does:

<script type="text/javascript">
    function toggleMenu(id){
      element = document.getElementById(id);
      element.className = (element.className.toLowerCase() ==
                            'expanded' ? 'collapsed' : 'expanded');
    }
    </script>
[download]

Notice the </script> tag moved to the end of the function definition. (Why didn't I notice this before?)

If anyone can shed light on this, I'd be most grateful.