The file is now /etc/thunderbird/pref/thunderbird.js and in the source is: https://anonscm.debian.org/cgit/pkg-mozilla/thunderbird.git/tree/debian/thunderbird.js
I added this to /etc/thunderbird/pref/thunderbird.js:
pref("mail.compose.other.header", "X-Debbugs-Cc");
restarted Thundebird, and it was there; super nice ! Please add it !
Paolo
