Just tried the acid2 test on Firefox and you're right, it doesn't work. Tried it with Konqueror 3.5.8 and it got 99% of it working, but the top of the smilie isn't in the right place.

A comment on Opera 9.5: After a while, the black bar that shows the tabs hurts the eyes if the site you are on has a light colored background... I might mod the interface...