Review for ToggleReplied by Jonathan Kamens
Rated 5 out of 5 stars
This is a great add-on, but unfortunately it's incompatible with the current versions of Thunderbird and SeaMonkey and its maintainer has disappeared: the web site is down and his email address bounces.
I've taken over maintenance of the add-on and created a new version which is compatible with current Thunderbird and SeaMonkey:
https://addons.mozilla.org/thunderbird/addon/togglereplied-2/
To create your own collections, you must have a Mozilla Add-ons account.