There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own.

https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites

https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message

https://support.mozilla.org/en-US/kb/connection-untrusted-error-message

Websites don't load - troubleshoot and fix error messages

http://kb.mozillazine.org/Error_loading_websites

• MOZILLA_PKIX_ERROR_MITM_DETECTED
• uses an invalid security certificate SSL_ERROR_BAD_CERT_DOMAIN
• configured their website improperly

How to troubleshoot the error code "SEC_ERROR_UNKNOWN_ISSUER" on secure websites https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER

I don't think this fix my issue, as a said before, i don't have any of this software nor any software that have capability to intercept secure connection.

Any help please?

What are your protection programs?

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

Hi NotReality_, we need a little more information to diagnose this.

When you are viewing the error page, and click the "Advanced" button, then click

SEC_ERROR_UNKNOWN_ISSUER

to expand another panel showing a coded version of the certificate Firefox refuses to accept. You can copy that certificate and paste it into a reply for a volunteer to decode and review.

Or try it yourself on a site like the following and look at the "Issuer" section:

https://certlogik.com/decoder/

You can check if there is more detail available about the issuer of the certificate.

• click the "Advanced" button show more detail
• click the blue error text (SEC_ERROR_UNKNOWN_ISSUER) to show the certificate chain
• click "Copy text to clipboard" and paste the base64 certificate chain text in a reply

If clicking the blue error text doesn't provide the certificate chain then try these steps to inspect the certificate.

• open the Servers tab in the Certificate Manager
  • Options/Preferences -> Privacy & Security
    Certificates: View Certificates -> Servers: "Add Exception"
• paste the URL of the website (https://xxx.xxx) in it's Location field

Let Firefox retrieve the certificate -> "Get Certificate"

• click the "View" button and inspect the certificate

You can see detail like the issuer of the certificate and intermediate certificates in the Details tab.

jscher2000 said

Hi NotReality_, we need a little more information to diagnose this. When you are viewing the error page, and click the "Advanced" button, then click SEC_ERROR_UNKNOWN_ISSUER to expand another panel showing a coded version of the certificate Firefox refuses to accept. You can copy that certificate and paste it into a reply for a volunteer to decode and review. Or try it yourself on a site like the following and look at the "Issuer" section: https://certlogik.com/decoder/

Sorry for a very, very late respond. I need to goes offline for few days.

As you ask, here the certificate.

Certificate Checks Status Check Information Valid To 30 Jan 2019 ( 57 days ) Weak-Key Does not use a key on our blacklist - this is good Key-Size 2048 bits Signature Algorithm Strong (sha256WithRSAEncryption)

Certificate Summary Subject RDN Value Common Name (CN) www.google.com Organization (O) Google LLC Locality (L) Mountain View State (ST) California Country (C) US

Okay, as i recall there was a site that make me suddenly redirected. After that, i find a strange activity in my Task Manager, you know some kind of background app. Maybe that is the problem?

The certificate issuer information looks normal, and I think Firefox should accept that.

Do you want to try deleting the cert9.db file and having Firefox regenerate it? The steps for that are mentioned in this article: What do the security warning codes mean?

NotReality_ said

Okay, as i recall there was a site that make me suddenly redirected. After that, i find a strange activity in my Task Manager, you know some kind of background app. Maybe that is the problem?

If you think your system might have become infected, please see: Troubleshoot Firefox issues caused by malware.

Okay, thank you, i already solve the problem.

I run a small scan using a newly downloaded Malwarebytes, and then it find many Adware and other Malware too. Now, i able to connect to Google and any major site freel just like before.

Thank you for all your help.