Because of Opera returning wrong value of window.height() (it returns html height instead) overlay is not actually centered with top: 'center'

it's possible if you have long document (3 screens) and you are on the top of it overlay will appear on the 2nd screen so you can't see it

My solution is manual defining var center for all except opera and 50% for opera

see http://www.pithill.org/kuvat/opera9.5_jquerybug.png