The boxes are a bit too wide and overlap the right column.
Seems to be a firefox-only issue.
Removing from .box div { both the display (inline-block) and the width (100%) seems to fix it.
Are you seeing that on the site or your local ?
mmm... looks like here is fine...
/me goes copy better the css. :P
I seem to recall I may have tweaked the css on the site when I added the home page, but that was in and amongst fighting with the redirects from / to /community ... I'll grab whats on the site and copy it to the repo O:-)