jQuery code working in Safari and Chrome but not Firefox

I'm got a site that has a long list of tweets, and as you scroll down the right column follows you down, showing stats on the tweets. (See it in action at http://www.grapevinegame.com . Click 'memorise', then 'skip' to get to the list page. Works in Safari and Chrome).

I'm using jQuery to update the top-margin of the right column, increasing it as I scroll down. It seems to be working fine in webkit-based browsers, but doesn't budge in Firefox. Heres the code, the right column element is a div with id = "distance".

// Listen for scroll function
            $(window).scroll(function () {

                    // Calculating the position of the scrollbar
         开发者_开发技巧           var doc = $("body"), 
                    scrollPosition = $("body").scrollTop(),
                    pageSize = $("body").height(),
                    windowSize = $(window).height(),
                    fullScroll = (pageSize) - windowSize;
                    percentageScrolled = (scrollPosition / fullScroll);

                    var entries = $("#whispers-list > li").length;

                    // Set position of distance counter
                    $('div#distance').css('margin-top', ($("#whispers-list").height()+$("#latest-whisper").height()+33)*percentageScrolled);

                    // Update distance counter
                        $('#distance-travelled').text(Math.round(distanceTravelled*(1-percentageScrolled)));            
                        $('#whispers-list li').each(function(index) {

                                //highlight adjacent whispers                               
                                if ($('#whispers-list li:nth-child('+(index+1)+')').offset().top >= $('#distance').offset().top && $('#whispers-list li:nth-child('+(index+1)+')').offset().top <= $('#distance').offset().top + $('#distance').height()) {
                                    // alert("yup");
                                    $('#whispers-list li:nth-child('+(index+1)+') ul').fadeTo(1, 1);
                                } else {
                                    $('#whispers-list li:nth-child('+(index+1)+') ul').fadeTo(1, 0.5);  
                                }
                              });               

                    });

Appreciate any help or advice!

Updated!

It seems that $("body").scrollTop() is always returning 0 which I assume is the problem.

But when I tried $("html").scrollTop() it seems to be returning the correct scrollTop.

Try changing the scrollPosition line to this:

scrollPosition = $("html").scrollTop(),