Rated 5 out of 5 stars

In reply to gmeades's post, the reason we need a contacts sidebar is that it is stupid to have to create a dummy email simply in order to be able to look up someone's telephone number, or postal address, or to see the notes in their contact record. The logical place for a contact sidebar that contains all of the above information is to the left of the inbox, not within an email, and that's why the Contacts sidebar transformed Thunderbird from a decent but flawed email client into an excellent one. Why Thunderbird's developers haven't made this functionality available in the core product is beyond my understanding. I hope the developer of the add-on makes it work with TB 52 soon, as I am greatly missing having it's functionality.