One wise step often: take a look at the header -- a fragment from your target follows:

<iframe src="javascript:false" title="" style="width: 0px; height: 0px
+; border: 0px none; display: none;"></iframe>
<script type="text/javascript" async="" src="//cdn.optimizely.com/js/2
+04774041.js"></script>
....
[download]

But, as it turns out, there are several threads here about similar problems, of which, this is one: Request by LWP Useragent refused by the web server but not by others.

That was found with Super Search -- a feature here that you'll often find helpful if you're careful about picking your search_terms.