root@pi:/opt# cat /etc/apt/sources.list
#deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free rpi
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
#deb-src http://archive.raspbian.org/raspbian/ jessie main contrib non-free rpi
#deb http://ppa.launchpad.net/ubuntu-mozilla-security/ppa/ubuntu trusty main
#deb-src http://ppa.launchpad.net/ubuntu-mozilla-security/ppa/ubuntu trusty main
#deb http://ppa.launchpad.net/mozillateam/thunderbird-next/ubuntu trusty main
#deb-src http://ppa.launchpad.net/mozillateam/thunderbird-next/ubuntu trusty main
deb http://archive.raspbian.org/raspbian stretch main contrib non-free
deb-src http://archive.raspbian.org/raspbian stretch main contrib non-free
#deb https://wiki.debian.org/DebianExperimental
#deb http://http.us.debian.org/debian/ testing non-free contrib main
#deb http://ftp.us.debian.org/debian testing main contrib non-free