I'm on 56.0.2 (64 bit) and even the addon page says "this addon is not compatible with your version..." + I tried installing but it does NOT delete the cookies (for example I set it for 3 min but after 3 min all my cookies were kept tight).

Fix it please!

EDIT: I refreshed the firefox and then tried the addon and it works. I believe it was the config that I made from the suggestions at privacytools.io (under "Firefox: Privacy Related "about:config" Tweaks") caused the incompatibility.