bypass-paywalls-firefox-clean/options/clearCookies.js

var ext_api = (typeof browser === 'object') ? browser : chrome;

window.localStorage.clear();
sessionStorage.clear();

var cookie_domain = getCookieDomain(document.domain);

// send domain to background.js (to clear cookies)
ext_api.runtime.sendMessage({
    domain: cookie_domain
});

function getCookieDomain(hostname) {
  let domain = hostname;
  let n = 0;
  let parts = hostname.split('.');
  let str = '_gd' + (new Date()).getTime();
  while (n < (parts.length - 1) && document.cookie.indexOf(str + '=' + str) == -1) {
    domain = parts.slice(-1 - (++n)).join('.');
    document.cookie = str + "=" + str + ";domain=" + domain + ";";
  }
  document.cookie = str + "=;expires=Thu, 01 Jan 1970 00:00:01 GMT;domain=" + domain + ";";
  return domain;
}

var msg = "Cookies (and local storage) removed from " + cookie_domain;
showMessage(msg, 2000);

function showMessage(msg, duration) {
    var el = document.createElement("div");
    el.setAttribute("style", "position:fixed;top:40%;left:40%;z-index:99;padding:4px;font-family: Arial, sans-serif;font-size:18px;color:white;background-color:blue;");
    el.innerText = msg;
    setTimeout(function () {
        el.parentNode.removeChild(el);
    }, duration);
    (document.body || document.head || document.documentElement).appendChild(el);
}