Why is firefox ignoring option selected on certain select name values?

Question

HTML

Wrote the following:

<form action="#" method="post" enctype="multipart/form-data">
      <label class="visually-hidden">Лейбл
        <select autocomplete="on" id="wellPosition" name="wellPosition" size="1" required>
          <option value="" disabled selected>Вместо плейсхолдера</option>
          <option value="first">Вариант 1</option>
          <option value="second">Вариант 2</option>
          <option value="Новая Москва">Вариант 3</option>
        </select>
      </label>
    </form>

Chrome, edge - norms, firefox stubbornly gives out an option with the value "New Moscow". Or, if there is no such option, it leaves the default field empty.
As soon as I change the select name to "Position" - everything works the same with blink-browsers.

<select autocomplete="on" id="wellPosition" name="Position" size="1" required>...

No, autocomplete="off" doesn't work. Checked.
Tell, knowledgeable people, what is happening with Firefox differently and at what level?

Answer 1

because the standard does not define what to do if a fool decides to use them - disabled and selected are mutually exclusive attributes