You are defining margins to body
, but it doesn't have a defined width. Using FF22's element inspector, for example, one can see that it is way more narrow than it should be (it doesn't even wrap your main div).
Since your wrapper
div is set at 866px, something like body { width: 866px; }
and, as @Sam R. noted, defining auto
margins to it (margin: auto;
or margin-left: auto; margin-right: auto
) would suffice. If you want to make it a little better, you could resize your divs relatively (e.g. 100%) after that.