We bought and installed a Comodo RSA positivessl certificate on our Server. When we enter our domain into the browser the certificate is accepted with Firefox 55.0.3 on Mac But ther are still some issues with Firefox on Windows. Somtimes we get the error "sec error unknown issuer" with a FireFox browser under Windows. We installed the same version of FireFox (55.0.3) and on one computer the certificate is working and on the other one we get the unknowen issuer error and have to accept the certificate manually. Does anyone know how to solve this problem?