>Our cross signature is not yet in place, however this certificate is fully functional for clients with the ISRG root in their trust store. When we are cross signed, approximately a month from now, our certificates will work just about anywhere while our root propagates.
>Let's Encrypt hasn't yet been added as a trusted authority to the major browsers (that will be happening soon), so for now, you'll need to add the ISRG root certificate yourself.