"(or use a css sprite)"

You mean like this one... http://smyfaceimages.s3.amazonaws.com/moods_orange.png ?

(yes, it's a bit of a mammoth image, but that's animation for you...)

Why did you choose to divide the image into lines? Wouldn't one long line (or tall column) make the code a bit simpler?

I had it as one tall column originally, but it turns out that one particular browser (Firefox, I think it was) refuses to render 44200px-high images.

> refuses to render 44200px-high images

COWARD!

hm strange. for me, the first time I loaded the page and whizzed the slider back and forth, it felt like each face was loading separately (faces were half-loaded etc).

or it could have been just the large sprite was still downloading as I was sliding the bar.

in which case, probably best to preload it :)

Are you on a slow connection? Has always seemed fine here. Or perhaps that s3 bucket is not near your part of the world, so a bit slower for you than me