jnb_autofill_branch_001.user.js

// ==UserScript==
// @name           jnb_branch_001
// @namespace      http://github.com/ymorimo
// @description    Autofill JNB's branch number 001 on its login form
// @include        https://www.japannetbank.co.jp/login.html
// ==/UserScript==
window.addEventListener('load', function() {
    document.forms.wrappedJSObject.HOST.TenNo.value = '001';
}, false);