How to Troubleshoot the Error Code “SEC_ERROR_UNKNOWN_ISSUER” on secure websites as Mozilla Firefox

The Websites which appears on Mozilla Firefox that supposed to be secure, must satisfy that the certificates presented by this website is valid. If the provided certificate is not validated, Firefox will represents some error messages that displayed as “Your Connection is not secure”. You might see some error code as “SEC_ERROR_UNKNOWN_ISSUER” on your websites. Hence, you should solve this problem as soon as possible.

What do you mean by this Error Code?

During a secure connection, a website always need to provide a certificate issued by a trusted “Certificate Authority”, in order to ensure that user is getting connected to the prescribed target and the connection is encrypted. If you see “Your Connection is not secure” error page and get the error code “SEC_ERROR_UNKNOWN_ISSUER”, after you click on “Advanced”, then it means that the certificate that were issued by a certificate authority, is not known by Mozilla Firefox, hence cannot be trusted by default by its user.

Your Connection is not secure

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In other words, it can be said that when Firefox connects to secure website, it must verify that the certificate that were presented by this website is valid and its encryption is strong enough to adequately protect your privacy. Hence, if the proposed certificate cannot be validated or the encryption is not strong enough, Firefox will stop the connection to the website and will show its error page.

If you get this error on particular site, it indicates that the web server is not configured properly. The trusted website ‘s certificate that have not been issued by a trusted certificate authority itself and no complete certificate chain to a trusted authority was provided either. You should contact the owner of the website and inform about the error.


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If the particular website allows, you can add an exception in order to visit the site, inspite its certificate is not being trusted by default.

Step 1:- You have to click “Advanced” on the warning page.
Step 2:- Then click “Add Exception”. An Add Security Exception dialog will appear.
Step 3:- Then read the text that describes the problems with the website. You can even click on View in order to inspect untrusted certificate as well.
Step 4:- After that click on Confirm Security Exception, if you are sure and want to trust the site.

How To Trouble Shoot the “Secure Connection Failed” Error Messages?

If your Firefox can’t access a secure site, you will see an error page with the heading Secure Connection Failed and a error message about the error.

confirm security exceptions

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Certificate Warnings:-

Mozilla Firefox uses certificates on secure websites to ensure that your information is being sent to the intended recipient and can’t be read by anybody.

Certificate will not be valid until date:-

This error basically occur if your respective computer clock has wrong date, in which the date given in the error message will be in the past. Hence, to fix this problem, you have to set your system clock to today’s date and time.

Certificate expired on date:-

This error basically occurs when a web-site’s identity certification has been expired. It can also occur, if your clock shows wrong dates. Hence, to fix this problem, just set your system clock to today’s date and time.

Certificate is not trusted because the issuer certificate is unknown

Suppose the file menu.db in your profile folder may get corrupted in your system. Just delete this file while Firefox getting closed.

Step 1:- Just open your Profile Folder.
Step 2:- Then, click on menu button, and then click on Help Button, then select “Troubleshooting Information”. A Troubleshoot window will appear on your screen.
Step 3:-Under the Application Basics section, you have to click on Open Directory. A window with your Profile File will be open.
Step 4:- Click on Menu button and then click Exit.
Step 5:-Then tap particular file name.
Step 6:-Press Delete
Step 7:-Restart your Firefox.

Certificate is not trusted because no issuer chain was provided

You have enabled SSL scanning in your security software. You should try to disable this option.

Certificate is not trusted because it is self-signed

self signed

Here, self-signed certificates make your data safe from malicious doers, but can’t say anything about the person who received the data. Its common for Intranet websites that are not available publicly.

Certificate contains the same serial number as another certificates

This particular error will alerts you the fact that, the certificate page you are visiting, uses a serial number that were identical to one who have already accepted. User will see this error message when they are attempting to access router’s configuration page.

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Bypassing the Warning:-

User can tell the Firefox to bypass these certificate warnings. Hence, you should only bypass the warning if you are sure that the particular site is legitimate. Legitimate Public sites will not ask you to do this. An invalid certification that can be indicated as web page that will be defraud you to steal your identity.

Step 1:-On the warning page, you have to click “Or you can add add an exception”.
Step 2:-Just click on Add Exception. After that, this Add Security Exception dialog will appear.
Step 3:-Then click on Get Certificate.
Step 4:-After that, just read the text describing the problems with this site.
Step 5:-Click on Confirm Security Exception, if you want to trust the site.