Hi MirceaForce, There is a possible fix of SEC_ERROR_REUSED_ISSUER_AND_SERIAL error in Firefox on test server. Could you try to do the following, please: 1. Make sure the issue is still reproduced. PC reboot may be required because the error could disappear after some time of working at PC. Launch anti-virus, run Firefox and try to open websites which are expected to be affected with the issue. 2. Run databases update from test server (note, we cannot guarantee absolutely correct pro