This Repo provides two Files which provides the ability to disable the signing check of Firefox for AddOns.

This file belongs in following path to be functional:

config.js -> C:\Program Files\Mozilla Firefox\ or C:\Program Files (x86)\Mozilla Firefox
config-prefs.js -> C:\Program Files\Mozilla Firefox\defaults\pref

You also need to edit the user.js or toogle following line in the about:config

xpinstall.signatures.required = false

(A Restart of Firefox is required, to make this work!)