You will need to install a user script manager extension to install this script.
Amazon added a subdomain that allows you to support local organizations through every purchase. Unfortunately, this only works if Amazon is used through this special subdomain and usually people link to normal amazon or you are used to typing just that in your browser. Since the functionality between both sites is virtually the same, a simple URL replacement works just fine.
There is no data sent to any server and everything happens client side.