> Websites prove their identity via certificates. Firefox does not trust https://www.mail-archive.com/dev-security-policy@lists.mozil... because its certificate issuer is unknown, the certificate is self-signed, or the server is not sending the correct intermediate certificates.
The certificate is issued by Let’s Encrypt [2], and has a valid and correct intermediate chain from the server [1]. Have you knowingly altered your browser’s TLS security settings, or certificate root store settings (for example, to distrust X3), or are you running an especially old browser on an out-of-date platform? Being able to see a screenshot of which intermediate your browser is refusing to trust would be helpful [3]. (Unless you’re somehow being MITM’d, which can happen on some internet connections or with certain ‘security’ software on Windows or by mitmproxy left enabled, in which case the screenshot of the certificate chain will look nothing like Let’s Encrypt at all and help diagnose that too.)
I am using a mobile browser,it could be out of date but I didn't tinker with the network settings. I doubt only this site would get MITM'd. I will see if I can get more details from it.
I would say with near certainty that your issues stem from your OS/browser, or if you have any security apps installed, those could be at fault too (since they sometimes run network interception). You might test a browser that ships its own SSL stack (I believe Firefox Android does, though I’m not 100% certain) and see if it Just Works in that, but at the end of the day, I’d simply recommend backing up your data and settings, factory resetting the device and updating it to latest, and then restoring your data and settings — there’s far too many things that can go wrong, especially in rooted scenarios, and I don’t have the ability to triage and repair beyond highlighting the three possible vectors you could tackle exploring yourself.
