Firefox doesn't trust to the certificate generated by Letsencrypt


Some instances of Firefox recognize certificate as untrusted. Issue affects Firefox versions 40, 42, 43. Weird but on another PC running Firefox 42 everything works just fine. Notice that the same certificate is trusted by Google Chrome, MS Edge. My page is
Yesterday (12/15/2015) certificate was trusted for all my PCs running different versions of Firefox.

See screenshots below:

Here is snapshot from Firefox which doesn’t rust to the certificate and one which trusts:

Did anybody face similar issue? If so - how to solve that?


Well… It’s not the Let’s Encrypt certificate to begin with… So no clue what’s wrong…


Would you explain how had you identify that?


OP said the Letsencrypt certificate for his server at wasn’t trusted by Firefox. When I go to that site it has a Comodo certificate, not a Letsencrypt certificate.


I was told that It was generated by Let’s Encrypt. My bad.
But still have you seen such behavior? And what is this failure caused by?


The only times I’ve seen a browser not accept the LE cert as valid is when it’s been installed incorrectly ( i.e. the relevant diferent certs haven’t been put in the correct places on the server). Exactly which ones should be used where depends on your system ( apache / nginx etc ) and version.