javascript countdown script from milliseconds in to hours-minutes-seconds

I am looking for a easy way to output milliseconds into hours-minutes-seconds. I have seen some plugins but i dont want to use a plugin in a plugin, and I have seen a lot of countdown snippets but these are using the date, I am using not a date but milliseconds.

Thanks.

EDIT: i am looking for a script that counts back from xxxx milliseconds to zero

//until now i have this

    diff  = 100000000;

    function showTimer() {

        hours = Math.floor( diff / (1000*60*60) );
        mins  = Math.floor( diff / (1000*60) );
        secs  = Math.floor( diff / 1000 );

        $('.count').html(hours+ 'hours' +minutes + 'minutes' +seconds + ' seconds');
    }

    setInterval(function(){showTimer()}, 1000 );