Can't find source of javascript error

Greetings! I am trying to find out the source of the following error on this website.

The piece of code we are looking at (I am using Firebug) is first found in the #coupons section. It is the piece of code that attaches the third coupon, dubbed Rightcoupon. Clicking on the image opens up the coupon. Here is the code:
<a href="https://lewisvilleairconditioning.com/coupons/Rightcoupon.jpg" onclick="window.open(this.href, '', 'resizable=no,status=no,location=no,toolbar=no,menubar=no,fullscreen=no,scrollbars=no,dependent=no,width=620,height=400'); return false;">
Here is the issue:
The problem is that this code also attaches itself to every other div following it– from the end of #coupons, to #main, #content-wrapper, #content, #post-5, .entry, and on down through the headings.

I have a basic understanding of code, and it looks like the aforementioned code is being attached due to a javascript error.

This is a custom template, and for whatever reason, the company has no relationship with them anymore. I have combed through all the files I can think of– header, page, footer and so forth.

How do I troubleshoot this issue? I have never seen anything like this before.

Thanks –Blake