Torbirdy: Enable the gpg_already_torified setting in the system configuration (refs: #15091, #15600).
There's:
/usr/share/xul-ext/torbirdy/defaults/preferences/000system.js → /etc/xul-ext/torbirdy.js
which is read after:
/usr/share/xul-ext/torbirdy/defaults/preferences/prefs.js
but setting extensions.torbirdy.gpg_already_torified to true in the former
doesn't seem sufficient, even though strace confirms it's being read.
Without this setting, fetching key from a keyserver doesn't work out of the
box.