In tribute to the late Sir Terry Pratchett many users are adding the message "GNU Terry Pratchett" into the email header "X-Clacks-Overhead". This plugin allows you to see when an email is using the header and read the message included.
Download the latest release directly from the Mozilla Addon site
Concept: Richard Atha-Nicholls Art: Amy Atha-Nicholls Original Firefox extension: Rob Grundy
This extension is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at https://mozilla.org/MPL/2.0/.