Revise prefs adopted from TorBirdy
_Originally created by @segfault on [#17268 (Redmine)](https://public-redmine-archive.tails.boum.org/code/issues/17268)_
When we adopted the prefs from TorBirdy in tails/tails#17220, a few things were
left unclear, marked with XXX in `config/chroot_local-includes/etc/thunderbird/pref/aa_tails.js`.
### Related issues
- **Related to** tails/tails#17220
issue