modules overlapping in firefox

I am using the right column position in the template. I have have five active modules in the position. If you look at the 3rd and 4th modules, the 4th module overlays the 3rd module. They are custom HTML modules, but there is nothing fancy in them. Has anyone else seen this happen? I never seen this with a commercial template.

I am only seeing this behavior in Firefox 16.0.2. The behavior does not present itself in Chrome or IE.

Any help is appreciated.

here is the site: dev25.janetdenison.com

Blessings,

I added the css clear property to mega-right id and megamodule class in the joomla.css stylesheet.