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SEC_ERROR_UNKNOWN_ISSUER with self-signed cert

  • 1 reply
  • 1 has this problem
  • Last reply by kede81

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I'm setting a staging server on a VM, and issued a self-signed certificate.

When accessing firefox is giving me the following error:

" The owner of has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website.

This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox may only connect to it securely. As a result, it is not possible to add an exception for this certificate. "

Clicking on Advanced shows:

" uses an invalid security certificate. The certificate is not trusted because it is self-signed. Error code: SEC_ERROR_UNKNOWN_ISSUER "

There is no way to add an exception.

I went into Preferences-Certificates-View Certificates / Servers-Add Exception. Typed "", clicked on Get Certificate-Confirm Security Exception. But I got the same message

Restarted FF. Same message. Checked in SecurityPreloadState.txt but cannot see mention of ""

Kindly indicate me how to add an exception for my staging site.


Modified by randoum

All Replies (1)

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HSTS is a configuration of the web server. See for details. It would appear that the server you are staging employs this mechanism. There is no error in how Firefox behaves, this is mandated by the HSTS standard as described in the Wikipedia article. I see three workaround options: 1. you import the self-signed cert as a CA cert in to your browser. That way I expect the certificate will be accepted (as the issuer is trusted) and therefore the connection should proceed. Note I haven't built a test environment to duplicate your setup and tried this out, so this is from theory only and I may be wrong. 2. you configure the staging server differently from the production server in not employing HSTS. This will permit the browser to ask you for a security exception. Please do not deconfigure HSTS from your production server, as it is a good idea, it just doesn't permit the staging setup you employ. 3. if your staging server has internet connectivity and you are able to assign a valid and internet-reachble DNS name, you could obtain a proper certificate for it, e.g. using, a free service.