Close to being so good it should be shipped with TB Rated 5 out of 5 stars
This extension shows an odd problem in the traditional UI design of Thunderbird: Namely, that it could be vastly improved.
Thunderbird Conversations has good selection of typical tweaks (displaying attachments, youtube embeds inline, hiding quoted email garbage) and packs the conversation window with exactly what is necessary without compromising screen space.
It almost integrates well with EnigMail, with the exception of the inline composition view -- and that's my only wish atm: Make a setting to disable the inline reply compose view.
Not just another add-on Rated 5 out of 5 stars
This is an add-on that greatly alters the usability of my mail application. "Conversation" has made my working patterns much more efficient, especially due to:
1) I read the WHOLE thread. I no longer have to leave the current view to browse my Sent folder. This was a huge problem before.
2) I can write my reply while staying in the Conversation view and keeping an overview of the previous items. I can even click another thread in the Inbox and go back to the previous thread without loosing text that I was typing.
Furthermore, it retains easy access to the normal composition window.
A big thank you to the author!