Images links work on IE but not in firefox or Chrome

Question

I have some social media buttons at the top of my companies website. They link to the various social media pages and work in IE but do not work in Firefox or Chrome. I cannot work out why this is. I have looked in the CSS but can't see what it is.

The links at at the top of the site next to the company logo which the link works and is the same set up. http://www.pareto.co.uk

Answer 1

The <div id="topNav"> that lays over the images and intercepts all click events.