Palemoon browser can run User JS a.k.a. browser scripts a.k.a. Greasemonkey scripts

Palemoon is based on the old Gecko Firefox code and it natively supports User JS scripts.

Just create a directory named guerillajs in your Palemoon profile directory and drop your user scripts there. As I said, there is no need for an add-on or extension like Greasemonkey or Tapermonkey.

I did this earlier and it did not work. Apparently, the scripts need the @include statement without which they do not work. I noticed an error message about this in the Browser Console of the browser. After I added the required @include statements, they all started working. Scripts that need to work on all websites also need @include statements as in:

// ==UserScript==
// @name          Universal.UserJS
// @namespace     com.vsubhash.js.universal.user.js
// @description   This User JS runs on all pages.
// @include       https://*
// @include       http://*
// @version       1
// @grant         none
// ==/UserScript==

document.addEventListener("readystatechange", onLoader, false); 
iRndm=Math.round(1000 + Math.random()*1000);

function onLoader() {
    try {
        if (document.readyState == "complete") {
          window.setTimeout(doTesting, iRndm);
        } else {
            console.error("Universal.UserJS: Not loaded");
        }
    } catch(e) {
        console.error("Universal.UserJS: " + e);
    }
}

function doTesting() {
    //console.log("Universal.UserJS: Hello");
}