In your style.css you have:
Code:
#sidebar.four.columns {margin-left: 1.6%; width: 32.6%; right: -.2em;}[line 111]
#sidebar.four.columns {margin-left: 1.5%\9; width: 32.6%; right: -.2em;}[line 112]
Code:
@-moz-document url-prefix() {[line 118]
#sidebar.four.columns {margin-left: 1.5%; width: 32.6%; right: -2px;}
#sidebar_left.four.columns {margin-right: 1.5%; width: 32.6%;}
}
Chrome is parsing all this to apply a left margin of 1.6% because it's ignoring 112 as invalid. You can see this using Inspect Element in Chrome. FF, at least, parses it at 1.5%, both because it is parsing line 112 despite the error, and also because of the (unnecessary) Mozilla specific code at 118. You can see this in Firebug/Inspect Element.
That extra 0.1% in Chrome is causing the float drop.
Sort out the errors here, get rid of the moz stuff, and use a single consistent styling using 1.5% margin and it should be OK.