Display the X-Clacks-Overhead in Clacks Semaphore (addon/extension for Firefox)

In tribute to the late Sir Terry Pratchett many websites are adding the message "GNU Terry Pratchett" into the html header "X-Clacks-Overhead". This plugin allows you to see when a website is using the header and read the message included. The message is also displayed visually in the semaphore style from the upcoming board game "Clacks" by Backspindle Games.

Concept: Richard Atha-Nicholls
Art: Amy Atha-Nicholls
Coding: Rob Grundy

This is NOT the official repository of the gnu_terry_pratchett firefox addon/extension.
I simply downloaded the xpi installation file, renamed the extension to .zip, extract & here it is!

Oficial developer: https://addons.mozilla.org/en-GB/firefox/user/11544584/
Oficial extension link: https://addons.mozilla.org/en-GB/firefox/addon/gnu_terry_pratchett/