Why I am getting the "Your connection is not secure" error screen in Firefox?

You will see the "Your connection is not secure" error screen in Firefox, if Firefox failed to validate the server certificate provided by the Web site you are visiting. One of the reason for the validation failure is missing the root CA certificate in Firefox as shown in this tutorial:

1. Run Firefox and go to "Tools > Options" menu.

2. Click "Advanced > Certificates" tab and "View Certificates" button.

3. Click "Authorities" tab and select "VeriSign Class 3 Public Primary Certification Authority - G5".

4. Click "Export..." button to save a copy of this CA certificate to a file called "VeriSignCA.crt".

5. Click "Delete or Distrust..." button to delete it from Firefox.

6. Close Firefox and start it again.

6. Visit Web site "https://www.paypal.com". You see the "Your connection is not secure" error screen showing up. It says:

The owner of www.paypal.com has configured their website improperly. 
To protect your information from being stolen, Firefox has not 
connected to this website.

This site uses HTTP Strict Transport Security (HSTS) to specify that
Firefox only connect to it securely. As a result, it is not possible
to add an exception for this certificate.

The picture below shows you the "Your connection is not secure" error page:

You know why. Because you deleted the root CA certificate from Firefox. Don't worry, you can import it back to Firefox by following the other tutorial.

 

⇒ Add Certificate Exception in Firefox

⇐ Export Server Certificate Full Path in Firefox to File

⇑ Managing Certificates in Mozilla Firefox

⇑⇑ Firefox Certificates Tutorials