WooCommerce : Disable Autofocus on the First Name field under Billing and Shipping address.

functions.php

<?php
/* Disable autofocus on the billing First Name field */
add_filter('woocommerce_billing_fields','disable_autofocus_billing_firstname');
function disable_autofocus_billing_firstname($fields) {
    $fields['billing_first_name']['autofocus'] = false;
    return $fields;
}

/* Disable autofocus on the shipping First Name field */
add_filter('woocommerce_shipping_fields','disable_autofocus_shipping_firstname');
function disable_autofocus_shipping_firstname($fields) {
    $fields['shipping_first_name']['autofocus'] = false;
    return $fields;
}