This page lists some thunderbird extensions I have either written or modified slightly.
This addon shows a ‘reply-to’ column in the message-list, you can sort on this column.
The code is mostly ripped from: http://developer.mozilla.org/en/docs/Extensions:Thunderbird:customDBHeaders_Preference
To enable it, set the following pref:
mainnews.customDBheader = ‘reply-to’ and install the .xpi.
Rebuild the folder-index to see the reply-to’s on older mails, new mails should show reply-to’s immediately.
Signature is an addon by ‘miek’, and can be found on the mozilla addon site. However, it hasn’t been updated in a while and doesn’t support thunderbird 2.x. This local copy has been patched to work with firefox 3.x and thunderbird 2.x.