Remove the OpenSearch <link> tag to prevent Google Chrome from auto-adding custom search engines.
// ==UserScript==
// @name Disable OpenSearch
// @namespace Disable OpenSearch
// @version 1.0
// @description Remove the OpenSearch <link> tag to prevent Google Chrome from auto-adding custom search engines.
// @author Snie
// @match http*://*
// @grant none
// ==/UserScript==
(function() {
'use strict';
var elOpenSearch = document.querySelector('[type="application/opensearchdescription+xml"]');
if (elOpenSearch) elOpenSearch.remove();
})();