Following the update of WordPress perhaps a feature in one of the plugins has stopped.
Reviewing the page errors with the browser inspector shows the error
$.browser is undefined
I have also encountered the $.browser is undefined error when I took over a website and updated the jQuery references as a part of my initial actions.
With the introduction of jQuery version 1.9 jQuery browser was no longer supported.
To our rescue is a set of scripts called jquery-migrate. The aim of which is to add back in those missing functions. Allowing more time for the changes to jQuery to be incorporated.
To add migration support add
<script src=”http://code.jquery.com/jquery-migrate-1.0.0.js”></script>
to the web page. Take care in its position on the page to get the sequencing right.
$.browser was used to determine which browser was in use, visiting the web page.
