Literally add document.oncopy=null to pages.
// ==UserScript==
// @name oncopy=null
// @namespace https://github.com/zamber/oncopy-null
// @description Literally add document.oncopy=null to pages.
// @version 0.1
// @author http://piotr.zaborowski.pro/
// @encoding utf-8
// @license https://creativecommons.org/licenses/by-sa/4.0/
// @homepage https://github.com/zamber/oncopy-null
// @twitterURL https://twitter.com/zamber
// @supportURL https://github.com/zamber/oncopy-null/issues
// @include http://*/*
// @include https://*/*
// @grant none
// ==/UserScript==
(function() {
'use strict';
document.oncopy = null;
})();