Looking at your site, I see two things that you can fix.
The main part of the page is shifted to the right (at least in Firefox) by the width of the text in the header navbar. This has a huge line-height (I don't know if it is in the original) and with a large font is causing a problem. Find and edit this in your stylesheet:
Code:
#navMain ul, #navSupp ul, #navCatTabs ul {
margin: 0;
padding: 0.5em 2em;
list-style-type: none;
text-align: center;
line-height: 4.5em; /*make smaller - 2.5em works*/
}
The sidebox heading backgrounds are fixed-size images, and when the font-size increases, they no longer fill the heading space. You can edit the images in Photoshop to enlarge them, or you can shrink the line-height or margins of h3.leftBoxHeading and h3.rightBoxHeading.