UPDATE: The problem seems to have finally resolved itself. Keeping this post live so you can see the things that you may encounter with going off the “approved platform”.
Just so you are aware, mobile variants of Firefox seem to dislike the SLL certificate for this site and are throwing errors over the place since about 9pm central time when you try to load the site. It may also appear in desktop variations of the site, which seems to have been fixed by clearing the browser cache for the site. That solution does not appear to work with the mobile version, however.
Chrome and Edge seem to work just fine. I have not checked Safari.
From what I have been able to discover, there was a hotfix update to all versions of Firefox to address a “zero-day exploit” around the same time as this problem came up for me. My security certificate is independently confirmed to be valid, but Firefox appears to think otherwise.
It might be a matter of another update, or that Firefox needs to update the SSL certificate definitions that are valid, something I have zero control over. If you are experiencing difficulties viewing the site with Firefox, I recommend using another browser for the time being; on desktop, go to the padlock in the site address and clear cache and cookies for the site when prompted, which seems to force a refresh of the SSL certificates.
Owning a domain is just fun, innit?