Lightbox used to be nice when it made one particular thing easy to do. Then it expanded to do five million things and became so complex that if you want to do any particular one of those things it's much easier to just code it by hand.
How queer. That suggests to me an issue with the way the browser is reporting the scroll position. HMMM :(
I've also just found out that IE9 displays all images at the same size as whichever image you click first. This is most vexing :@ (and best of all it works just fine in IE8 :? )
IE is more diabolically cruel than waterboarding...
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"Cellphones have turned people blessed with opposing thumbs and ten digits into monkeys hammering on a 2-inch touchscreen with all the speed and grace of a retarded badger molesting a tennis ball."
Heh. Turned out that assigning a new src to an existing image object doesn't update the width and height properties in IE9. Fixed it now, anyway (by creating a new image object each time).
If you expand this (I presume you'll want to add fading in and out? People seem to expect that these days) .. try not to go too far and end up being what lightbox is. This should be the "I just want it to work without a lot of fucking around" option. So not too many settings and tasteful defaults.
</telling you to do stuff you probably already knew>