Here is the information

Try to rename the cert8.db file in the Firefox profile folder to cert8.db.old or delete the cert8.db file to remove intermediate certificates that Firefox has stored.

If that helped to solve the problem then you can remove the renamed cert8.db.old file.
Otherwise you can rename (or copy) the cert8.db.old file to cert8.db to restore the previous intermediate certificates.
Firefox will automatically store intermediate certificates when you visit websites that send such a certificate.

You can use this button to go to the Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

@cor-el

Sorry that did not resolve the issue

I get redirected automatically from the blog.mozilla.com to the blog.mozilla.org domain.

Try to use the Forget About This Site button to remove all stored data from the blog.mozilla.com domain.

You can inspect and manage permissions for all domains on the about:permissions page via the location bar.

On the about:permissions page I removed all blog* and *mozilla* entries and tried again: [Social API] but this still throws up the same security issue as I had originally.

even if I paste the above link in directly I get the issue.

I will also pursue the issue with the software that is alerting me to the problem.