http://www.africanbushcamps.com/abc/ If you check with FF 3.5.16 (you can use the portable version to see), you'll see the left sidebar is in place, content and right sidebar goes down.
I'm suspecting it might be some width confusion with left sidebar but can't get to solve it... Any ideas or common FF 3.5 bugs you know like this?
It seems to be a problem with the float layout.
You should definitely use inline blocks for your columns, here's some links that will help you getting it working.
http://blog.mozilla.com/webdev/2009/02/20/cross-browser-inline-block/
http://www.highchairdesign.com/studio/inline-block