Try to rename the cert9.db file (cert9OLD.db) and remove a possible previously used cert8.db file in the Firefox profile folder with Firefox closed to remove intermediate certificates and exceptions that Firefox has cached.

• https://support.mozilla.org/en-US/kb/what-does-your-connection-is-not-secure-mean

If this has helped to solve the problem then you can remove the renamed cert9OLD.db file. Otherwise you can undo the rename and restore cert9.db.

You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page (Root directory).

• Help -> More Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

well it didn't work. i also reinstalled the app. when i import the certificate it doesn't show up in my certificate manager's list. see the screenshots, when the certificate imports properly it locates after "netlock kft" but as you can see nothing shows up here.

Do you see any kind of error message when importing the certificate? Are you sure you are importing the correct one?

What kind of certificates is this about? Isn't this about about a certificate in one of the other categories?

Under Authorities normally only intermediate certificates would appear and current releases download these intermediate certificates automatically to the security_state folder.

• https://wiki.mozilla.org/Security/CryptoEngineering/Intermediate_Preloading