jQuery.support.fixedPosition Original Code: http://kangax.github.com/cft/#IS_POSITION_FIXED_SUPPORTED

jQuery.support.fixedPosition.js

(function($){
    $(function(){
        $.support.fixedPosition = (function(){
            var container = document.body;

            if (document.createElement && container && container.appendChild && container.removeChild) {
                var el = document.createElement('div');

                if (!el.getBoundingClientRect) return null;

                el.innerHTML = 'x';
                el.style.cssText = 'position:fixed;top:100px;';
                container.appendChild(el);

                var originalHeight = container.style.height,
                originalScrollTop = container.scrollTop;

                container.style.height = '3000px';
                container.scrollTop = 500;

                var elementTop = el.getBoundingClientRect().top;
                container.style.height = originalHeight;

                var isSupported = (elementTop === 100);
                container.removeChild(el);
                container.scrollTop = originalScrollTop;

                return isSupported;
            }
            return null;
        }());
    });
}(jQuery));