Firefox SEC_ERROR_UNKNOWN_ISSUER Easily [Solved]


Mozilla Firefox is a web browser which you use, here are many error occurs with error code or without error code. One of the errors is Firefox sec_error_Unknown_issuer. Many people troubled with this issue when they use Firefox. When you see this error message that means you are not able to open web-pages. Suppose, you work on some important topic and sudden this error occurs on your system, then it will get frustrating for you. Read this full article to fix this Firefox error.

What is the cause that Firefox sec_error_unknown_issuer occurs on my browser:-

For connecting securely, websites need to provide a certificate that is issued from the certificate authority to ensure that it is connected to the target website and the connection is also encrypted. If the connection is not encrypted then it shows you an error saying Firefox sec_error_unknown_issuer when you try to open a website. That means the Firefox connection is a default connection and not trusted because the certificate is unknown.

It is mainly a website’s or browser’s responsibility to explore or provide a secure issued certificate. But, if any virus or malware is available in your system then it also causes the Firefox error.

But no need to panic, read this full article to fix this Firefox error.

Solutions to fix Firefox sec_error_unknown_issuer:-

Here are many easy and quick solutions to fix this error. Follow the below-given steps:

  1. Remove browser history of Firefox:-

    • At first, open Mozilla Firefox and tap on the menu bar (three horizontal lines) which is at the top-right corner of the screen to open the menu.
    • Now, click on History and select Clear browsing data.
    • Choose All and tap on the Clear
    • Now, tap on Settings and situate the Change Proxy
    • After that, navigate to the Security and Privacy section and tap on the Medium
    • Now, close your web browser and re-open again. And, open that website to check if the error is fixed now.
  2. Make a new user profile:-

    To creating a new user profile you can fix the Firefox sec_error_unknown_issuer easily. Follow the below steps:

    • If Firefox is already open then tap on the menu bar (three horizontal lines) and tap on Exit to close Firefox. If Firefox already closed in your system then go to the further steps.
    • Press Windows key + R simultaneously to open the Run dialogue box.
    • Now, enter exe –P and tap on OK option.
    • A Firefox – Choose User Profile windows will pop-up.
    • Now, tap on Create Profile.
    • After that, go through with the on-screen instruction to complete the process.
    • Re-open your Mozilla Firefox and login to your new user profile.
    • Now, open the website and check if the error has been fixed.
  3. Run a virus scan on your system:-

    • It may be possible that there is a virus in your computer and it clogs the website to detect the certificate so the Firefox sec_error_unknown_issuer occurs. Viruses also cause the error itself.
    • So, for fixing this problem try to run a virus scan across your entire system. It will take some time to complete so be patient. It may be possible that the windows defender is not able to detect error so it tries to search out any antivirus to detect the error.
    • If you find any malware in your system, then follow the on-screen instruction which is provided by the antivirus program to fix the error.
    • Once you finish the error, then reopen your system and open the website again in Firefox to check if the error has been resolved now.
  4. Disable SSL scanning from your antivirus software:-

It may also happens that your antivirus program clog your computer to navigate the website without issued certificate. So, disable SSL scanning from your antivirus software to open the website which gives Firefox sec_error_unknown_issuer.

As you know, there are many antivirus programs. I will explain to you to disable SSL scanning from your antivirus software by taking an example of Avast antivirus software.

    • At first, launch Avast antivirus on your system and tap on the menu bar which is at the top-right corner of the screen.
    • Tap on the Settings option from the menu list.
    • Now, tap on Components which is on the left side of the screen and select Customize in the Web Shield
    • After that, a pop-up window will open, uncheck the box next to the Enable HTTPS Scanning from here.
    • Tap on OK
    • Tap on OK again to save the changes.
    • Now, re-launch Firefox again and open the website to check if the error has been fixed.


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