• Click on star of address in message reader's header adds to "Personal Address Book".
• Contextual Add to Address Book does the same.
• (Enterprise) user cannot change the target AB for manually added contacts.

Enterprise users will probably not be happy with all of their manually added contacts ending up in Personal AB. I think we should implement a pref with UI to choose a custom default AB for that action, like we currently have a UI pref to change the target AB for Collected Addresses.

Here's how the new pref could look.
Of course, we can tweak the label:

• Default address book for manually added contacts (see mockup)
• Default address book for adding contacts (I like that, short and simple).

The AB from the suggested pref will also be used when focus is on All Address Books and you create a new contact.

Actually I expected changing the preference "Default startup directory in the address book window" to my default address book to also change where addresses are saved by default, but that is not so...

It's normal to use carddav or other synced address books these days, and to want one such as default. Getting rid of the extra clicks when adding contacts would be a nice enhancement to Thunderbird.

In other words: I would like to see this feature implemented!