openssl req -x509 -nodes -days 1095 -newkey rsa:2048 -keyout server.key -out server.crt

All of a sudden (i.e. not after a Firefox upgrade) Firefox 41.0 has stopped accepting self-signed SSL certificates on various websites which it had been accepting for months. I've generated the certificates myself. The link / button to add exceptions and import the certificate has disappeared from the "Untrusted Connection" error page. Things I've tried so far: * Import the certificates via Preferences > Advanced > Certificates > View Certificates > Servers. The certificates get imported but Firefox seems to ignore them. * Quit Firefox, delete cert8.db from my profile, then restart Firefox * Restart Firefox in Safe mode * Import the certificate in the OS Keychain (this makes the websites work on Chrome and Safari) The generated certificates are signed with "PKCS #1 SHA-256 With RSA Encryption", they are not expired and were generated with openssl req -x509 -nodes -days 1095 -newkey rsa:2048 -keyout server.key -out server.crt Apart from the trust issue, https://www.ssllabs.com/ssltest/ reports no problem whatsoever with these certs, they are fine ("If trust issues are ignored: A") The only way I can access these websites is via a Private Browsing window: if the certificate was previously imported (via Preferences) the private session window can access the websites without a problem. If the certificate wasn't imported yet I get the option to add a temporary exception and after that is done it works fine. This problem doesn't appear on another computer, even though the Firefox profile is synced between the two. The problem does not appear on a colleague's Firefox 41.0 (same OS and hardware) Certificates signed by a real CA are accepted just fine. UPDATE: I've marked this as resolved, but apparently the problem keeps coming back about once a week, in a completely random manner. The best solution I've found so far is to quit Firefox, delete the following files from my profile, then restart Firefox: * SiteSecurityServiceState.txt * cert_override.txt * cert8.db