I don't know JavaScript at all, så please bare with me

I've added a JavaScript widget to this page:

The widget-code is:
<div id="nav_stillinger"></div>
<script src="https://tjenester.nav.no/stillinger/widget?sort=akt&amp;rpp=50&amp;p=0&amp;l2=63218&amp;rv=al" type="text/javascript"></script>
The widget works when I paste the code inside a empty HTML-document, so I suspect that it's "allergic" to the HTML-document. Debugging in Firebug gave me this error:
HierarchyRequestError: Node cannot be inserted at the specified point in the hierarchy
Line 11
Any help would be appreciated.