I don't have a Mac and I've never used one, so this is somewhat hearsay. For a long time, the Mac address book was read-only in Thunderbird. So to manage it, you'd have to access it via whatever tools OSX offers you for this. ISTR that in a recent Thunderbird, this might have been fixed, so it is possible that it should now be able to edit and delete OSX address book entries from within Thunderbird. Another possibility is that Thunderbird's own address book is corrupted. The usual symptom is that users can edit their Contacts, but when Thunderbird is closed and restarted, it reverts to the state it was in prior to the editing. That is, the changes weren't written to disk. I'm not confident this applies to you, as you don't seem able to make ''any'' changes. As a check, if you drag a Contact from the OSX address book to one of Thunderbird's native address books, are you then able to edit the copy? (If you hold down control {command?} while dragging, it should make a copy. If it doesn't have write permission on the OSX address book, it will copy regardless, since it isn't permitted to delete the original in the OSX address book.) One way to fix a corrupt address book is to export it and import to a new address book. Ideally you would also close Thunderbird, locate the broken address book file in Thunderbird's profile and delete it. There is some advice [http://chrisramsden.vfast.co.uk/11_Thunderbird_Settings_and_the_Profile.html here] about exporting and importing address books.