message: Fix `mark-unread`
  Fixes
diff: @@ -37,13 +37,12 @@ function stripHash(url) {
  }
  function addMarkUnreadButton() {
  - const container = select('.js-thread-subscription-status');
  - if (container && !select.exists('.rgh-btn-mark-unread')) {
  + if (!select.exists('.rgh-btn-mark-unread')) {
  const button = <button class="btn btn-sm rgh-btn-mark-unread">Mark as unread</button>;
  button.addEventListener('click', markUnread, {
  once: true
  });
  - container.after(button);
  + select('.thread-subscription-status').after(button);
  }
  }
  