Thunderbird 102 - Firstly thanks for finally integrating the address book into a tab.
Within address books you can search contacts via inputting text. However there is no quick way of cancelling this search other than manually deleting the text in the search box.
An 'X' along side would be handy, and perhaps a 'PIN' similar to how message searches/filters are either carried over to other mailboxes or not.
Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.