Solution to Overcome SEC_ERROR_UNKNOWN_ISSUER on Firefox

Solution to Overcome SEC_ERROR_UNKNOWN_ISSUER on Firefox

In total, there are various types of problems that can occur in the Firefox browser. But most of them are very rare or almost never experienced. If anything happens, it’s caused by settings only and of course it can still be overcome.

Like a notification appearsSEC_ERROR_UNKNOWN_ISSUER“This is very rare. And if this happens to the device you are using, it may be because there is a missing certificate data (missing).

If this problem is present when you are doing related testing proxy, then this is perfectly normal. It’s because of the proxy require certificate (SSL) installed to be able to access HTTPS-based sites. Meanwhile, if you’re not doing any testing, it’s possible that the problem is caused by another program, such as an antivirus or a proxy/VPN manager program.

Don’t worry, because here I will share some solutions to overcome it. Please follow starting from the first solution.

1. Install Certificate in Firefox Manually

This first solution is only for users who are testing proxy. For example, I just bought a proxy and installed it to access a website, but failed due to the SEC_ERROR notification appearing.

So the solution is to install the certificate from the proxy. You can get it from the proxy service provider. And to install it is very easy, just follow the steps below:

  1. open Options on Firefox.

  2. In the search field, please type Certificate.

  3. Then click on the button View Certificates.

  4. On tab Authorities, click button Import.

  5. Now locate and select the downloaded certificate file.

  6. Then a dialog will appear, please check the two options that appear, and then press the button Import one more time to add it.

  7. Done, the certificate was successfully added.

After doing the steps above, try to access a website. If the certificate added is correct, surely there will be no more error messages in Firefox, and you can access HTTPS-based sites without any more problems.

2. Turn off the HTTPS Scanning Feature in Antivirus

Some antivirus programs such as ESET, Avast, or AVG has a feature named HTTPS Scan. Actually, this feature has a good intention or purpose to ensure the website visited is really trusted.

So when the website you visit has an untrusted SSL certificate, the antivirus will block access to the website and a SEC_ERROR notification appears in the browser.

To get around this, you can temporarily disable the HTTPS Scanning feature on the antivirus while accessing the website. Or if the website feels really safe, please add an exception to the antivirus, so that there are no more scans when accessed.

3. Stop the Process of Proxy/VPN Programs

Who would have thought if this problem was caused by the proxy manager program or connection to the VPN network that you are using on the computer. For example, don’t realize if you’re activating Proxifier, and its kind. Or there is a malfunction of the VPN program that affects the internet network being used.

Therefore, try to re-check the process of any proxy/VPN program that is currently running through Task Manager, and then stop.

Also read: How to Use Tamper Data in Firefox Quantum

4. Reinstall Firefox

If the three methods above have been done but the error notification still appears, I highly recommend reinstalling the browser. Most likely the certificate data in the browser is lost, so all websites that are accessed appear to be from untrusted certificates, so the browser refuses to continue.

Of course, reinstalling the Firefox browser will restore the lost certificate data.


In conclusion, the problem of the emergence of errors SEC_ERROR_UNKNOWN_ISSUER on Firefox this refers to an unrecognized certificate (SSL). The problem can be caused by the proxy used, or the certificate in the browser is missing. But by trying some of the steps above, I guarantee the problem can be solved.

Hopefully useful and good luck

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