原因
火狐自帶自動填寫表單功能，
How to Turn Off Form Autocompletion
("https://developer.mozilla.org/en-US/docs/Web/Security/Securing_your_site/Turning_off_form_autocompletion")
解決
form上增加控制
<form method="post" action="/form" autocomplete="off">[…]</form>
元素上增加控制
<form method="post" action="/form"> […]
<div> <label for="cc">Credit card:</label>
<input type="text" id="cc" name="cc" autocomplete="off">
</div>
</form>
