privateWindowHomepage.uc.js

// ==UserScript==
// @name           Private Window Homepage
// @version        1.1.0
// @author         aminomancer
// @homepage       https://github.com/aminomancer/uc.css.js
// @description    By default, private windows are opened to <about:privatebrowsing>, regardless of your homepage or new tab page preferences. Once the window is opened, opening a new tab goes to your new tab page, and pressing the home button goes to your actual home page. But the first tab of a private window is always opened to about:privatebrowsing. This behavior is coded right into `OpenBrowserWindow()` but we can change it. This script simply removes the part of the function that manually sets the URL to about:privatebrowsing. So private windows will now behave like ordinary windows in this (and only this) respect.
// @downloadURL    https://cdn.jsdelivr.net/gh/aminomancer/uc.css.js@master/JS/privateWindowHomepage.uc.js
// @updateURL      https://cdn.jsdelivr.net/gh/aminomancer/uc.css.js@master/JS/privateWindowHomepage.uc.js
// @license        This Source Code Form is subject to the terms of the Creative Commons Attribution-NonCommercial-ShareAlike International License, v. 4.0. If a copy of the CC BY-NC-SA 4.0 was not distributed with this file, You can obtain one at http://creativecommons.org/licenses/by-nc-sa/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.
// ==/UserScript==

(function () {
  const lazy = {};
  XPCOMUtils.defineLazyServiceGetters(lazy, {
    BrowserHandler: ["@mozilla.org/browser/clh;1", "nsIBrowserHandler"],
  });
  ChromeUtils.defineESModuleGetters(lazy, {
    HomePage: "resource:///modules/HomePage.sys.mjs",
    PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
  });
  function init() {
    if (BrowserWindowTracker.og_openWindow) {
      return;
    }
    BrowserWindowTracker.og_openWindow = BrowserWindowTracker.openWindow;
    eval(
      `BrowserWindowTracker.openWindow = function ${BrowserWindowTracker.openWindow
        .toSource()
        .replace(/^\(/, "")
        .replace(/\)$/, "")
        .replace(/^function[^\S\r\n]*/, "")
        .replace(
          /\N*\s*if \(\!args && \!lazy\.PrivateBrowsingUtils\.permanentPrivateBrowsing\) {(?:\n\s*\/\/.*)*\s*loadURIString \= \"about\:privatebrowsing\"\;\s*\}/gm,
          ""
        )}`
    );
  }
  if (gBrowserInit.delayedStartupFinished) {
    init();
  } else {
    let delayedListener = (subject, topic) => {
      if (topic == "browser-delayed-startup-finished" && subject == window) {
        Services.obs.removeObserver(delayedListener, topic);
        init();
      }
    };
    Services.obs.addObserver(
      delayedListener,
      "browser-delayed-startup-finished"
    );
  }
})();