In long PR changed files I see a huge slowdown from removing `intent-mouse` class #3028

  function focus_confirmation_buttons_init() {
    document.body.addEventListener("toggle", event => {
      const confirmButton = Object(select_dom["a"])('[open] details-dialog [type="submit"]', event.target);
      if (confirmButton) {
        setTimeout(() => {
          confirmButton.focus();
          document.body.classList.remove("intent-mouse");
        });
      }
    }, true);
  }
  features.add({
    id: "focus-confirmation-buttons",
    description: 'Always focuses confirm buttons in custom modal boxes, like "Mark all as read".',
    screenshot: "https://user-images.githubusercontent.com/1402241/31700158-1499bdd8-b38d-11e7-9aba-77a0a4b6bf3c.png"
  }, {
    load: features.onDocumentStart,
    init: focus_confirmation_buttons_init
  });