If you are trying to access site with self-signed certificate with Firefox 31 (or later) and get Issuer certificate is invalid error (sec_error_ca_cert_invalid), you have to disable new mozilla::pkix certificate verification.

In about:config set

security.use_mozillapkix_verification = false

To find out more about mozilla::pkix and why your firefox just got so super secure and paranoid, that it doesn’t allows you to access you own site without googling – see https://wiki.mozilla.org/SecurityEngineering/Certificate_Verification. I’m only wondering, why did they renamed it from insanity::pkix to mozilla::pkix – do they confess that ‘mozilla’ is slowly becoming a synonym for ‘insane’ ?-) Throwing such an error without any hint or possiblity to add an exception (as usual) is IMHO insane – but, who cares about power users today…

Update: As noted in comments, this should not work in Firefox 33 (or later).

Update2: As noted by #29 and referenced bugs, there seem to be (at least) 2 major cases, where new insane::pkix will refuse to accept a https site.

1. Your internal CA certificate doesn’t specifies CA:TRUE in X509v3 Basic Constraints section
2. You self-signed server certificate (the last one in certificate chain) specifies CA:TRUE – what is default for certificates generated by pkitool script from easy-rsa suite – and you have your CA certificate installed in FF.

See also FF bug #1042889.

Update3: Thanks to the work of Kai Engert, there is a fix for this in Firefox 31 ESR (download from https://www.mozilla.org/en-US/firefox/organizations/) and hopefully the same comes also with Firefox 33.1.