Configuration of public website

Hi there,
My public website is not accessible (just realized yesterday). Has something changed recently?
It says: “Your connection is not secure.
The owner of xxx has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website.
xxx uses an invalid security certificate. The certificate expired on April 10, 2018, 15:58. The current time is April 11, 2018, 10:48. Error code: SEC_ERROR_EXPIRED_CERTIFICATE”
Best and thanks,

What is your website?
(send in private message if you prefer)

Thanks for solving the issue!