Install Greasemonkey
To install Greasemonkey, go here :
https://addons.mozilla.org/fr/firefox/addon/greasemonkey/
Then click on Add to Firefox

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Install A4A801
To install A4A801, go here :
http://outil.derpolino.shost.ca/addon/A4A801.user.js
A window will open, wait for the countdown and click on Install

To see the source code, click here: Source code A4A801

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A4A801 is now installed!