The best thing I ever did for my parents was teach them to use different passwords everywhere. Against conventional wisdom, I get them to write them down in a book, because for them, keeping a book secure is much easier than knowing what to do to keep their computers secure. We already know how to keep physical objects reasonably secure, we do it every day with our credit cards, passports, jewelry etc.

Worse yet, some such sites intentionally break pasting into the password field, making it a pain to paste in a randomly generated password.

You can fix that with a bookmarklet to re-enable pasting.

  var inputs = document.getElementsByTagName('input');
  for (var i=0; i < inputs.length; i++) {
    if (inputs[i].getAttribute('type').toLowerCase() === 'password') {
      inputs[i].setAttribute('onpaste', '');
    }
  }