Poor carousel performance in chrome and firefox

Question

Im a javascript learner and i am trying to solve the following. I have created a carousel using a container with overflow scroll. Inside i have the carousel div containing all my items. All my items have opacity 0.3 except for one item which is within my "Focus Point". When the user scrolls i have a script that checks which item is within my "Focus Point".

var ItemToFocus = function(){
    if(  MousewheelActive == 1  ){

        First_Item_Offset = $Active_Carousel_Item.first().offset().left;
        First_Item_Offset = -First_Item_Offset;
        Focus_Point = 0.45 * Window_Width;
        Carousel_Position = First_Item_Offset + Focus_Point;
        Width = $Item.first().width();
        Length = $Active_Carousel_Item.length;

        for( i=0; i < Length; i++ ){
            Right = (i+1) *Width;
            Left = Right-Width;
            if( Right > Carousel_Position && Left < Carousel_Position ){

                if( ! $Active_Carousel_Item.eq(i).hasClass("Carousel_Item_Focus_Instant") ){
                    $Active_Carousel_Item.eq(i).addClass("Carousel_Item_Focus_Instant");

                    clearTimeout(Introduction_Timer);
                    Introduction_Timer = setTimeout(function(){
                        $Carousel_Item_Focus_Instant = $(".Carousel_Item_Focus_Instant");
                        $Carousel_Item_Focus_Instant.find(".Introduction").show();
                    },600); 

                } else if( $Active_Carousel_Item.eq(i-1).hasClass("Carousel_Item_Focus_Instant") ){
                    $Active_Carousel_Item.eq(i-1).removeClass("Carousel_Item_Focus_Instant").addClass("Carousel_Item_Blur").find(".Introduction").hide();
                } else if( $Active_Carousel_Item.eq(i+1).hasClass("Carousel_Item_Focus_Instant") ){
                    $Active_Carousel_Item.eq(i+1).removeClass("Carousel_Item_Focus_Instant").addClass("Carousel_Item_Blur").find(".Introduction").hide();   
                }

            }

        }

    }

Im basicly looping through each item and checking its Left and Right offset. This works great in Safari and Opera, but its laggy in Chrome and Firefox. My knowledge is limited when it comes to browser differences. Does Chrome and Firefox use more resources on the scroll method? If so is there a way that i can implement script that amends this so i can achieve a smooth scrolling experience? Here is a temporary link to the website, which mind you is very beta.

http://192.185.4.96/~andrewn8/

I would greatly appreciate some advice as im trying to learn as much a possible about this.