Find replace!.user.js

// ==UserScript==
// @name         Find replace!
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  tbodt's idea, but executed poorly
// @author       You
// @match        http://*/*
// @match        https://*/*
// @grant        none
// ==/UserScript==

let replace = {
    // "some key \(may include regex\)": "some value"
};

window.onload = function() {
    let walker = document.createTreeWalker(document.body, NodeFilter.SHOW_TEXT, null, false);
    while (walker.nextNode()) {
        let node = walker.currentNode;
        for (let key of Object.keys(replace)) {
            node.textContent = node.textContent.replace(new RegExp("\\b" + key + "\\b", "gi"), replace[key]);
        }
    }
};