FYI - "https-only" mode does not work the way you think it does ;) The site is hard to access on such browsers only because it actually does serve something over HTTPS - however, it's just an error page there.
Just because there is something on this domain listening on :443 and serving HTTPS, doesn't mean it has to serve the same content as the HTTP on :80, or even work at all.
Always-redirect-to-HTTPs plugins _are_ broken by assuming otherwise.
Author here. I took a look in IIS Admin and is unable to see WHERE did I ask it to serve https. I thought I was http only. The bindings only say http, both for the bef.no site and for the 'Default Web Site'.