I took some screenshots of the website. Running latest version of Firefox at a screen resolution of 1440x900.

Screenshot 1 & Screenshot 2

Firefox renders webpages/CSS as they're coded/defined. Internet Explorer has difficulty with the latest versions of CSS and cannot render them correctly, which is why your website looks fine in Internet Explorer but overlaps in Firefox. I recommend reading this article on Internet Explorer and CSS issues.

I ran the website through a validator and it came up with 677 errors & conflicts on the homepage alone. Having had a look through your HTML & CSS source code, there are quite a few conflicts -- most are relating to DIV classes and how they're executed in the HTML, others are down to the classes not being defined correctly in the CSS stylesheet.

The easiest option would be to scale down the homepage and redefine/revise the CSS classes in the stylesheet so content doesn't overlap and is aligned correctly across all browsers -- margin, padding & text-align are the main properties which you should utilise. Once you've redifined the CSS classes, you should ID the DIV tags with the correct classes.

If you require any help or tutorials feel free to email me.

I am having that exact same problem with google chrome.