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/