It seems only the 'https' site is gone, the 'http' site is still around[0].
Very useful for testing but don't make a habit to use it on some random websites.
I have the following all set to false in about:config
network.stricttransportsecurity.preloadlist
dom.security.https_first
dom.security.https_first_pbm
browser.fixup.fallback-to-httpsI’d forgotten all about this site, don’t remember ever using it but I certainly heard of it.