Letsencrypt ISPConfig 3 security error in Firefox

Question

I have setup SSL certificates with letsencrypt and ISPConfig 3 (on a cheap hosting service).

Installed letsencrypt on a Ubuntu desktop:

git clone https://github.com/letsencrypt/letsencrypt
cd letsencrypt
./letsencrypt-auto

Created the certificates:

./letsencrypt-auto certonly --manual

and filled out the fields in the SSL tab domain-settings in the ISPConfig hosting control panel.

Then I copied:

1. contents of /etc/letsencrypt/live/domain/privkey.pem to the SSL Key field
2. contents of /etc/letsencrypt/live/domain/cert.pem to the SSL Certificate field

And saved the certificates.

Now Opera, Chromium and Explorer all give a secure connection, but Firefox claims the connection is not secure.

How to fix that?

Answer 1

The solution is to copy the chain certificate too:

3. contents of /etc/letsencrypt/live/domain/chain.pem to the SSL Bundle field