Ajax not firing properly using Firefox, but works in Chrome

This is the barebones for an AJAX call and response. Take a look and make sure this is working on Chrome and Firefox for you — works for me.

<?php

// Some function for data we'll pass

function dgx_donate_get_countries_requiring_postal_code()
{
    return "cc postal code stuff...";
}

// Register everything

add_action('init', function () {

    // Add required scripts

    wp_enqueue_script('jquery');
    $script_url = plugins_url('/js/seamless-donations.js', __FILE__);

    wp_register_script('seamless_javascript_code', $script_url, array('jquery'), false);
    wp_enqueue_script('seamless_javascript_code');

    // Localize our data 

    wp_localize_script(
        'seamless_javascript_code', 'dgxDonateAjax',
        array(
            'ajaxurl' => admin_url('admin-ajax.php'),
            'nonce' => wp_create_nonce('dgx-donate-nonce'),
            'postalCodeRequired' => dgx_donate_get_countries_requiring_postal_code()
        )
    );

    // Register AJAX handlers

    add_action('wp_ajax_dgx_donate_paypalstd_ajax_checkout', 'dgx_donate_paypalstd_ajax_checkout');
    add_action('wp_ajax_nopriv_dgx_donate_paypalstd_ajax_checkout', 'dgx_donate_paypalstd_ajax_checkout');

    // AJAX handler (PRIV / NO PRIV)

    function dgx_donate_paypalstd_ajax_checkout()
    {
        // If we fail don't be silent 

        $fail_message="";

        if (empty($_POST['nonce']) || !wp_verify_nonce($_POST['nonce'], 'dgx-donate-nonce')) $fail_message="Bad Nonce";
        if (empty ($_POST['action'])) $fail_message="Missing Action";
        if ($_POST['action'] !== 'dgx_donate_paypalstd_ajax_checkout') $fail_message="Bad Action";

        // We failed, let em know...

        if (!empty ($fail_message)) {
            wp_send_json_error(array(
                'message' => $fail_message
            )); // die
        }

        // Do logic stuff

        // Send the Success Response

        wp_send_json_success(array(
            'action' => $_POST['action'],
            'message' => 'Checkout Complete',
            'postalCodeRequired' => $_POST['postalCodeRequired'],
            'ID' => 1
        )); // die
    }
});

// Shortcut to trigger AJAX call on page load

add_action('wp_footer', function () { ?>

    <script>

        (function ($) {

            var data = {
                action: 'dgx_donate_paypalstd_ajax_checkout',
                nonce: dgxDonateAjax.nonce,
                postalCodeRequired: dgxDonateAjax.postalCodeRequired,
            };

            $.ajax({
                type: 'POST',
                url: dgxDonateAjax.ajaxurl,
                data: data,
                success: function (response) {

                    // look at the response 

                    if (response.success) {

                        // succcess data
                        console.log(response.data);

                    } else {

                        // no good
                        console.log(response);
                    }
                }
            });

        })(jQuery);
    </script>
<?php });