src/background.js

function isEmpty(obj) {
  return Object.keys(obj).length === 0;
}

const defaultOptions = {
  'list': true,
  'thread': true,
  'threadall': false,
  'fixedtoolbar': false,
  'redirect': false,
  'history': false,
  'loaddrafts': false,
  'batchduplicate': false,
  'escalatethreads': false,
  'movethreads': false,
  'increasecontrast': false,
  'stickysidebarheaders': false,
};

function cleanUpOptions() {
  chrome.storage.sync.get(null, function(options) {
    console.log('[cleanUpOptions] Previous options', options);
    var ok = true;
    for (const [opt, value] of Object.entries(defaultOptions)) {
      if (!(opt in options)) {
        ok = false;
        options[opt] = value;
      }
    }

    console.log('[cleanUpOptions] New options', options);

    if (!ok) {
      chrome.storage.sync.set(options);
    }
  });
}

chrome.runtime.onInstalled.addListener(function(details) {
  if (details.reason == 'install' || details.reason == 'update') {
    cleanUpOptions();
  }
});

chrome.browserAction.onClicked.addListener(function() {
  chrome.runtime.openOptionsPage();
});