Why am I getting sec_error_unknown_issuer in Firefox?

Posted on 2009-04-27
Last Modified: 2013-12-07
We are getting a sec_error_unknown_issuer on ONE machine in the building using Firefox trying to get to  This machine is using Firefox 3.0.9.  Other machines using 3.0.9 do not have this trouble.

Where to begin?  What's going on?
Question by:mrcoulson

    Author Comment

    Okay.  I just installed 3.0.9 on another machine and this is happening there, too.  Hmmm.  But it's still only some machines.

    LVL 35

    Accepted Solution

    If you go to this address:
    and input "", then let it check the SSL, you see that the "certificate will not be trusted in all web browsers".

    This is true, because I tested it in Opera and it works fine. Why only a few Firefox machines at your place are affected, I cannot tell, my Firefox didn't like the certificate either. I assume it could have something to do with already having the certificate chain installed from earlier, versus going there first time.
    Maybe the server admin reinstalled/renewed the certificate and did not do it correctly?

    Anyway, here's the remedy:
    Go to Entrust's root certificate download page:
    on the Download page, scroll down to the last certificate (Entrust L1B Chain Certificate), right-click it and select "Save target as...".

    In Firefox, open Tools > Options > Advanced > Encryption > Show Certificates
    Select the tab "Certification Authorities" (last but one), click "Import" and point it to the .cer file you just downloaded from Entrust. Click 'Ok' a couple of times and restart Firefox.

    That solved the issue for me.
    LVL 35

    Expert Comment

    When importing the certificate, make sure to place a checkmark in for the kind of certification you wish (websites for sure, maybe email, too?)

    Author Closing Comment

    Bingo!  And thanks for the resource in


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