deb http://ftp.us.debian.org/debian stretch main
deb-src http://ftp.us.debian.org/debian stretch main

deb http://ftp.us.debian.org/debian stretch-updates main
deb-src http://ftp.us.debian.org/debian stretch-updates main

deb http://security.debian.org/debian-security/ stretch/updates main
deb-src http://security.debian.org/debian-security/ stretch/updates main

#Add buster to grab a functional firefox release
# /etc/apt/preferences prevents this from updating the whole system
deb http://deb.debian.org/debian/ testing main