Direct link to the live Observatory: https://observatory.mozilla.org/

Example run on addons.mozilla.org: https://observatory.mozilla.org/analyze.html?host=addons.moz...

The Observatory measures site's compliance with the Web Security guidelines [1] and the Server Side TLS guidelines [2]. It's primarily meant as a helper for website developers and operators.

[1] https://wiki.mozilla.org/Security/Guidelines/Web_Security

[2] https://wiki.mozilla.org/Security/Server_Side_TLS

(disclaimer: I work on security at Mozilla)