Message and News Reading
Thunderbird Conversations Featured
This addon provides a conversation view for Thunderbird, grouping messages together and allowing you to reply "inline" thus providing a more efficient workflow.
Persistent sticky notes for Thunderbird associated to mails.
In TB 78, you can define the note position in the settings. If you have a large screen, you can even display the notes outside of TB's main window, so it won't hide anything.