Firefox: Reset certificate database

I was testing a secure server connection over SSL with a self-signed certificate. Typically, Firefox would show a warning about the self-sign certificate along with an "Advanced" option which allows us to add an exception for the site. However, recently I ran into an error code: SEC_ERROR_REUSED_ISSUER_AND_SERIAL, which doesn't have the option to grant the exception. I tried going into the Certificate Manager and remove the previous exceptions but the error persisted.



I was able to resolve this by deleting the cert8.db which basically reset the certificate database. The cert8.db is located in your Firefox profile:
C:\Users\<username>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile_name>