scroll.user.js

// ==UserScript==
// @name         Remember scroll position
// @match        https://deeplearningwithpython.io/chapters/*
// @grant        none
// @run-at       document-idle
// ==/UserScript==

(function () {
  const key = 'scroll:' + location.pathname;

  function restore() {
    const saved = +localStorage.getItem(key);
    if (!saved) return;
    // retry a few times in case images/fonts are still shifting the layout
    let tries = 0;
    const iv = setInterval(() => {
      window.scrollTo(0, saved);
      if (Math.abs(window.scrollY - saved) < 5 || ++tries > 20) clearInterval(iv);
    }, 250);
  }

  if (document.readyState === 'complete') restore();
  else window.addEventListener('load', restore);

  let t;
  window.addEventListener('scroll', () => {
    clearTimeout(t);
    t = setTimeout(() => localStorage.setItem(key, window.scrollY), 300);
  });
})();