There are two default address books in Thunderbird. 'Personal Address Book' and 'Collected Addresses' You cannot remove these default address books. There is also a default virtual address book called 'All Address Books'.

By default if you add a contact it goes into the Personal Address Book and if you send an email to someone not in the Personal Address Book then those emails by default tend to be put into 'Collected Addresses'.

When you receive an email and it has an email address of a contact and you want them in your Personal Address Book, click on the 'From' email address in header area and select 'Add to address book' It auto is saved in Personal Address Book.

This is where you set up what address book you use for collecting outgoing mail and default start up address book.

• In 'Settings' > 'Composition'
• scroll down to 'Addressing' section
• Select checkbox: 'Local Address Books'
• Select checkbox: 'Automatically add outgoing email addresses to my' and select 'Personal Address Book' from the drop down options.
• Default start up directory in the address book window: select 'Personal Address Book' from the drop down options.

Thank You!