Apparently, Konqueror 3.5.1 is also ACID2 compliant. I have not used Konqueror for about a couple of years now. Recently I installed FreeBSD 6.1 and it came with KDE 3.5.1, so I gave it a try. I was really impressed. Of course the rendering speed of Konqueror is still quite slow by IE or Firefox standard. But sadly enough, neither IE nor Firefox is fully ACID2 compliant. Particularly IE is off by a large margin (literarily).
Here are the screenshots of the ACID2 tests on these three browsers:
Konqueror 3.5.1 ACID2 Test
Firefox 2.0 ACID2 Test
IE 7.0.5730.11 ACID2 Test