bg.js

chrome.tabs.onCreated.addListener((tab) => {
  // Only in tab restoration case is URL set at creation time -> defer to Chrome's default logic
  // (Surprisingly, url is not set at creation time for cmd-click opened tabs...)
  if (tab.url && tab.url !== 'chrome://newtab/') {
    return;
  }

  // Otherwise, new tab -> open to the right of last accessed
  let tabId = tab.id;
  let windowId = tab.windowId;

  chrome.windows.get(windowId, { populate: true }, (window) => {
    if (chrome.runtime.lastError || !window || !Array.isArray(window.tabs)) {
      return;
    }

    const candidate = window.tabs
      .filter(t => t.id !== tabId)
      .sort((a, b) => (b.lastAccessed || 0) - (a.lastAccessed || 0))[0];

    if (candidate) {
      chrome.tabs.move(tabId, {
        index: candidate.index + 1
      });
    }
  });
});