Ok so we're working on a class website and we have buttons that change the background and create, snow, leafs, or clouds.  We have the backgrounds in their own divs and in image tags.  We have it set up so the image tag has a 100% width and height so it fills the whole browser window.  When we do that, it makes the snow and leaf fall VERY laggy.  When we take the picture and shrink it down to like 10% the snow and leafs work fine.  Does anyone know how we can have a full sized background and not have it lag the snow?  Why does having a full sized background make it lag in the first place?  That doesn't make sense to me.  We've also preloaded the images including the background pictures so I am at a total loss...  Here's our website:

http://247designstudios.com/site/2/#

Just click on the "Winter on" or "Fall on" buttons to see the laggyness.  But when you resize the browser window, the background fills the whole screen up, which is good, we just dont want the lag!  Any help would be extremely appreciated.  Thanks.

Mr. Kidd

**Update**
So we opened it in Google Chrome and it works perfectly...  So that's telling us that Firefox and IE can't render it fast enough????  Is there a way to make firefox work faster?  We're totally lost here.