Hi Adam Sorry to hear about this error you're having. Let's check up on a couple of things. First of all, your post is tagged with Linux, so what distribution are you using? Second of all, your version is tagged as Firefox 91.0, are you using the stable or ESR (Extended Support Release) version? Can you duplicate this on an updated version of Firefox (currently 95.0)? Finally, are you logging in directly from getpocket.com, or from a bookmark?

There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own. https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites https://support.mozilla.org/en-US/kb/secure-connection-failed-firefox-did-not-connect https://support.mozilla.org/en-US/kb/websites-dont-load-troubleshoot-and-fix-errors [https://support.mozilla.org/en-US/kb/what-does-your-connection-is-not-secure-mean What do the security warning codes mean]