I have a valid letsencrypt certificate for my NS 7.3 server installed and default. I show a secure connection in Chrome, IE, Edge, but in Firefox I get the following error; office.mydomain.com uses an invalid security certificate. The certificate is not trusted because the issuer certificate is u…

I’ve encountered this with owncloud. I had to flush the cache in firefox then navigate back to owncoud. In my case it was where I was using firefox to configure the server prior to installing my certbot cert which held the self signed cert which caused the error once the proper cert was installed.

Letsencrypt certificate not secure in Firefox only

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phonon112358 (Aaron) March 5, 2017, 10:59pm 4

Perhaps, you could try to generate a new (stronger) certificate/key using certbot: