ThreadVis displays all messages in a conversation in a compact visual map, identifying the chronology of and contributors to a discussion and supporting navigating between messages in a thread.
Don't be distracted in your normal workflow. ThreadVis does not change the default layout of Thunderbird, it adds itself to unused space in the header bar.
Jump back and forth between messages in a thread, regardless of folder location. Don't be forced to keep all messages in a single folder to display the thread hiearchy, sort messages any way you like and still make sense of the context the mails were sent in.
Immediately see the different authors in a thread.
Make sense of longer conversations and see gaps in communication flow.
First things first: ThreadVis is free software. It's Open Source. As long as you comply with the license, you can do anything you want with it.
If you want to tell everyone how great ThreadVis is, rate the add-on at its addons.thunderbird.net home.
If even that is not enough:
GitHub