although I don't agree with the general markup, but it looks like you set the footer width = 100% PLUS padding-left = 15px !! which will always have the full width of the browser (due to the width: 100%) and another 15px! (this is not visible just because you are using overflow: hidden, but it is!) Try to remove the left pad and apply it to the inner element.
EDIT : after checking IE, this is not the reason for this, but is still bad practice.
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