Have you cleared your browser's cache and history? Both Opera and
Firefox (43.0.1 Windows) connect without complaint for me, showing the
Let's Encrypt certificate.

Perhaps Let's Encrypt isn't included in the default certification
authorities in your Iceweasel build (unlikely). Visit
https://letsencrypt.org and check the Support pages. --Don


Edward Bartolo wrote:
>Iceweasel version 38.5.0 is still refusing to connect to
>git.devuan.org insisting the site is untrusted. I am using Devuan 64
>bit.