In my earlier post, I provided the step-by-step instructions to host a website on an Apache web server and secure it thru HTTPS. I have found that the site works perfectly fine in IE and Chrome but it throws a certificate error while browsing it thru Mozilla. It throws the SEC_ERROR_UNKNOWN_ISSUER error.

If your application is calling APIs hosted on an HTTPS endpoint then it may not work because Mozilla will block the API calls due to this error. So if API is returning some data then that data may not appear on the webpage. In this blog post, we will resolve this issue.

STEP 1: Browse the site where this error is coming from and download the certificate as per the below screenshot:

Also, get the root certificate and intermediate certificates if it is not installed in your system.

STEP 2: In the Firefox address bar type this : about:preferences#privacy

Now import certificates downloaded in step 1.

STEP 3: Now restart the browser and open the HTTPS-enabled URL. You should not see SEC_ERROR_UNKNOWN_ISSUER certificate error and API calls will be successful.