For some reason I encountered this problem today - I normally let autocomplete choose the url for art of sound so perhaps has never before tried to used https:

When doing so I get this info:

Your connection is not secure

The owner of www.theartofsound.net has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website.
And from the Advanced tab:

www.theartofsound.net uses an invalid security certificate.

The certificate is not trusted because it is self-signed. The certificate is only valid for Parallels Panel The certificate expired on 25 July 2015 12:21. The current time is 10 April 2016 21:51.

Error code: SEC_ERROR_UNKNOWN_ISSUER
Do you have a security certificate for Art of Sound?