There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connections and send their own certificate. 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-error-message https://support.mozilla.org/en-US/kb/connection-untrusted-error-message http://kb.mozillazine.org/Error_loading_websites https://www.bing.com/search?q=SEC_ERROR_REVOKED_CERTIFICATE&pc=MOZI

https://forums.yahoo.net/t5/Password-and-sign-in/Secure-Connection-Failed-An-error-occurred-during-a-connection/td-p/504527 https://www.ssllabs.com/ssltest/analyze.html?d=mail.yahoo.com&hideResults=on An issue with some Yahoo pages.

I have this problem also as of today. Yesterday everything had worked fine. Haven't found an answer of how to fix it. I can access my Yahoo mail account without problems from Windows Edge browser.