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How to Fix Error Code SEC_ERROR_UNKNOWN_ISSUER in Firefox


Want to fix SEC_ERROR_UNKNOWN_ISSUER error in Firefox browser? Here is a short guide to solve this issue.

Errors can be a real interruption and pose a terrible effect on the workflow. Knowing the in-depth meaning of the error code or the message is crucial to avoid any form of hindrance during the operations.

Errors can be mentally draining, especially when you are not aware of the exact meaning. It is uncommon to even stumble upon one from time to time. This article helps you to solve this SEC_ERROR_UNKNOWN_ISSUER issue in Firefox.

Let’s quickly dive in and understand this error message in detail.


The SEC_ERROR_UNKNOWN_ISSUER is an error that is displayed to the user when the website in use does not offer a trustworthy SSL Certificate from a renowned SSL Certificate provider.

The growth in eCommerce has raised the concerns of the users related to security increasing the significance of SSL Certificates obtained from a trusted SSL Certificate provider.

In case, you are facing the SEC_ERROR_UNKNOWN_ISSUER issue in Firefox, it clearly implies that your SSL Certificate does not come from a reliable certificate authority (abbreviated as CA) as per Mozilla Firefox. This error is displayed as MOZILLA_PKIX_ERROR_MITM_DETECTED by Firefox too.

This error occurs when the SSL Certificate is issued by an authority that is unknown to the web browser. When the connection is secure, the website has to submit a certificate that is issued by a reliable authority so as to provide the verification. This is a mandatory step on most browsers including Mozilla Firefox.

The SEC_ERROR_UNKNOWN_ISSUER issue can also be interpreted as the error which the browser is not able to relate with a reliable CA on the basis of the details put forth by the eCommerce website browsed by you. It also means that the default connection is not trusted.

The pre-agreed obligations for the certificate authorities are firm and should be practiced by them in all situations. Any compromise is seen as a breach of the rules and results in strict measures. It should be ensured by the authorities that the certificate is fulfilling all the requisites and will not pose problems in the future.

What are the reasons behind SEC_ERROR_UNKNOWN_ISSUER error?

There are a set of reasons as to why the error code SEC_ERROR_UNKNOWN_ISSUER is displayed to you. Some of them are as follows:

  • Faulty antivirus software is the first reason SEC_ERROR_UNKNOWN_ISSUER is displayed to you by Firefox. In order to resolve this, one can reinstall their antivirus software. Reliable Microsoft software should be put to use instead of third-party antivirus products.
  • The unreliable self-signed SSL Certificates can be another reason for the error. These certificates have almost zero reliability and therefore these are not trusted by Firefox.
  • At times, the traffic monitoring and filtering tools utilized in the corporate spheres can intercept encrypted connections. This also involves placing their certificate instead of the original certificate of the website. In such cases, it displays errors even on secure HTTPS sites. These cases should not be ignored and one should get in touch with the IT branch in order to resolve the same.
  • Due to the absence of the important intermediate, SEC_ERROR_UNKNOWN_ISSUER is displayed to the users too.

How to fix SEC_ERROR_UNKNOWN_ISSUER in Firefox

Run a virus scan: 

An unknown issuer error can be caused due to a virus that resides in your computer system. It is necessary to run a virus scan to detect it and avert the certificate from being noticed. The virus sometimes creates an issue.

An antivirus can identify it and remove or fit it as per antivirus suggestions. It is suggested to go with paid antivirus as it comes with many features that a free version cannot provide. Once the issue is fixed, restart the computer, and open the website if it is fixed or not.

Create a new user profile: 

Firefox browse lets you create a new profile. A new profile can fix the error in Firefox. To do so, you need to follow the below steps.

  • First, close the Firefox browser and open the Run box with ‘’Window + R’’ and type firefox.exe -P, Click “OK“.
  • You will have a small box naming ‘’Choose Your Profile’’ where you need to click on “create profile” showing on the left side.
  • After that, you will have Create Profile Wizard window where you need to click on the “Next” button.

create a new user profile

  • After that, you will have a new box where you need to keep the desired name of your profile, click the “Finish” button.

create profile wizard

  • Now, restart the Firefox browser with the newly created profile.
  • Open the website and check if the error persists or not.

Disable SSL scanning in your antivirus software:

Antivirus generally comes with an option to scan HTTPS connections that should be disabled in your antivirus program. It prevents the certificate from being identified.

Once you disable the scan option in your antivirus, it will fix the error. The option of disabling scanning option may differ as per antivirus products. Once you disable the option, restart the Firefox browser, and access the website again.

disable scan option


Errors are the part and parcel of browsing on the internet. All the users come across a number of errors every day. One such common error is the SEC_ERROR_UNKNOWN_ISSUER. It shows the presence of unreliable certificate authority which may lead to a further threat to the security of the users.

As the SSL Certificates are really important because cybercriminals often exploit details such as usernames and passwords, private data such as names, residential addresses, date of birth, and email addresses of the users and cause substantial losses to them.

For being progressive in the market and ensuring the security of your business at the same time, it is essential to make use of present-day encryption technology. The SSL Certificate helps you in achieving strong rapport in the market and will attract the consumers towards the safer option being provided by you.

Similarly, when Firefox detects that the certificate is unreliable; it warns you of the error. One can follow the abovementioned steps to fix the same and work smoothly without any form of obstruction.

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