Review for Edit Email Subject (EES) by Richard Langner
Rated 5 out of 5 stars
I only found your add-on after I figured out how to do this manually. It's easy to alter 'To' and 'From' and 'Dates' too. Video is here https://www.youtube.com/watch?v=Yh0lUL9sOdg
This review is for a previous version of the add-on (6.2).To create your own collections, you must have a Mozilla Add-ons account.