The W3C (World Wide Web Consortium) site w3 org currently returns:
503 Service Unavailable
Word is that a bit earlier browsers were reporting certificate expired.
Yet another reminder that certs are a critical component of TLS (HTTPS).
Of course one could retain plain vanilla HTTP in parallel or as a fallback rather than simply 301-ing it to https.
Unfortunately browsers these days like to call such insecure even where there really is nothing (on the site) to secure; there may be a mitm! a monster under the bed!
Browsers as helicopter parents.