What’s the error message you’re seeing in Firefox?
Could you provide a screenshot of the certificate as shown by Firefox? (Click on the lock > arrow > “More Information” > “View Certificate”)? The PEM file would be fine too (Details > Export on the “View Certificate” window. It’s a text file - you can open it with any text editor and paste it here).
Which version of ESET NOD32 are you using?
Older versions of ESET had a SSL proxy which replaced any site’s certificate with a SHA-1 certificate. That might cause issues in some browsers.