Hello there ecl two. We have read your message. We try to help you. After installation, restart TB, then right-click a folder, Remove duplicates... The are more settings under Tools/Add-on Options. https://addons.thunderbird.net/en-US/thunderbird/addon/removedupes/ https://support.mozilla.org/en-US/kb/installing-addon-thunderbird https://www.thunderbird.net/en-US/thunderbird/releases/ https://archive.mozilla.org/pub/thunderbird/releases/ Greetings Firefox volunteer.