So I am currently using Ubuntu on my laptop and Debian on servers, and am in the process of getting more involved in Debian development. Debian uses SSL/TLS certificates issued by cacert.org which Ubuntu does not trust by default. Ubuntu does ship the cacert.org certificate in the ca-certificates package tho. So to get Chromium and Firefox to trust it, you have to do:
sudo apt-get install ca-certificates libnss3-tools certutil -d sql:$HOME/.pki/nssdb -A -t TC -n "CAcert.org" -i /usr/share/ca-certificates/cacert.org/cacert.org.crt firefox /usr/share/ca-certificates/cacert.org/*.crt
