At some point I disabled trust for this cert (along with many others - I distrust non-English CAs and those known to have been hacked). Then when I clicked "Get Add ons" I would get a failure connecting to services.addons.mozilla.org due to untrusted issuer. There is no option to "add exception" because the site uses HSTS, according to the msg. Outside of Firefox i had to use my own code to connect to services.addons.mozilla.org and debug the SSL/TLS handshake. I saw the root CA from the server and checked my Firefox trust store. Once I re-enabled trust for the DigiCert Global Root CA, I could successfully execute "Get Add ons". The point here is that you error screen is not helpful. Even if you do not want to let me add an exception, you should at least give me a clear option to view the cert chain. Otherwise how else can someone possibly fix this? Luckily I work with security stuff so could find the certs in the chain externally by other means. Thank you.