"autcollect addresses" prefs
from mailnews.js:
// by default, only collect addresses the user sends to (outgoing)
pref("mail.collect_email_address_incoming", false);
pref("mail.collect_email_address_outgoing", true);
pref("mail.collect_email_address_newsgroup", false);
// by default, use the Personal Addressbook for collection
pref("mail.collect_addressbook","moz-abmdbdirectory://abook.mab");
For the reasons why the defaults changed, see this document on the Collected Address Book.
There is UI for the "mail.collect_email_address_outgoing" pref. See "Edit | Preferences.. | Mail & Newsgroups | Addressing"
"other compose header" pref
from mailnews.js:
// you can specify a comma delimited list of optional headers
// this will show up in the address picker in the compose window
// examples: "X-Face" or "Approved"
pref("mail.compose.other.header", "Approved,X-No-Archive");