UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:47.0) Gecko/20100101 Firefox/47.0

Steps to reproduce the problem:
I have a client who use Chrome to use a web application.

Since the update to 51 last week, there is a part of the application that now no longer works. Its a Javascript function that now fails and the application hangs.

Everything still works on Firefox, IE, Safari and Chrome version 50

This is a massive issue.

The JS function that no longer works is below. This function, retrieves an updated list of customers & consumers from the database which then repopulates a form, appending the added customer/consumer.

I get NO errors from the Chrome Console????!!!!

        refresh_people: function (new_id) {
            $.post('/contacts/get_contacts_amended', {}, function (data) {
                $('#new_job_form #customer_name').empty();
                $(data.customers).each(function (i, item) {
                    var sel = (new_id == item.id) ? 'selected="selected"' : '';
                    $('<option value="' + item.id + '"' + sel + '>' + item.company + '</option>').appendTo('#new_job_form #customer_name');
                });
                $('#new_job_form #consumer_name').empty();
                $(data.consumers).each(function (i, item) {
                    var sel = (new_id == item.id) ? 'selected="selected"' : '';
                    $('<option value="' + item.id + '"' + sel + '>' + item.title + '. ' + item.forename + ' ' + item.surname + '</option>').appendTo('#new_job_form #consumer_name');
                });
                //$('#new_job_form #consumer_name_row').effect('highlight');
                //$('#new_job_form #customer_name_row').effect('highlight');
            });
        },

What is the expected behavior?
What happens on screen when this function operates correctly:

Overview of the functionality:

1) A user is adding a job to the system, a dialog box opens for them to enter details of the new job. (#new_job_form)
    a) - this includes a list of current customers (dropdown/select)

2) If the job relates to a new customer, there is a link on the add job dialog to create a new customer.

3) When the new customer link is clicked, a new dialog box appears on top of the add job dialog for them to enter the new customers details.

4) Once the user has entered the new customers details and clicks ok:
   a) - the customer is added to the database
   b) - the new customer dialog is closed
   c) - the new customer is appended to the list of current customers (dropdown/select) on the add job dialog

4c is the problem, appending the newly entered customer to the dropdown on thew add job screen

What went wrong?
The application just hangs

Did this work before? Yes on version 50 and all previous versions

Chrome version: 51  Channel: n/a
OS Version: OS X 10.10
Flash Version: Shockwave Flash 21.0 r0