I am running Thunderbird 139.0.2 (64-bit). I have two address books. In '''Tools > Settings > General > Message List''' the box beside '''Show only display name for people in my address book''' is checked. Nonetheless, the Message List Pane displays several Contacts in my Address Book with both full name and email address. If I right click on the name and email address in the Message Preview Pane and click '''Add to address book''' the name and e-mail address do not revert to Display Name only. If I right click them again there is still the '''Add to address book''' option, with no '''Edit Contact''' option, as if the Contact had not yet been added. In some cases after adding the Contact to the address book there is only the '''Display Name''' in the Message List Pane but this display name is neither of my address books.