On the page source, from line 90 onwards we have:

var pictureSrc = 'http://shii.org/b/mittens.gif'; //the location of the mittens
var pictureWidth = 40;            //the width of the mittens
var pictureHeight = 46;           //the height of the  mittens
var numFlakes = 10;               //the number of  mittens
var downSpeed = 0.01;          
var lrFlakes = 10;         
var EmergencyMittens = false;

I really want to fiddle about these settings. Especially numFlakes.