Maybe there's a feature or extension to do this ? Long time Tbird user. I have hundreds of mostly defunct collected email addresses. I won't use 99% of them again, but afraid to delete in case I might need one. They overpopulate the To: field when I start entering. I have a small personal address book, but those hits often come up AFTER the old collected ones. I have to look through. I'd like to archive 99% of these some way such that they don't appear in the To: field. I actually moved the old ones to a new address book that I called "Old Collected Addresses", but that did not help.