At first I thought it was going to be some kind of solution to force all linux apps to adhere to the XDG Base Directory Specification, until I realized this related to a different specification altogether (XDG MIME Applications specification).
Strange. Middle-clicking the link opens a HackerNews frontpage, but copypasting into a new tab shows the article. Presumably the server shoos away referer links? To reduce load maybe somehow? Or maybe something's weird in my own configuration idk.