Earlier this year both Opera and Webkit announced that they achieved a 100% score on the Acid3-test; a test designed to test standards compliance for webbrowsers. However, as you can see, just scoring 100% on the individual tests is not enough for a full pass; to completely pass on this test the animation has to look smooth as well.
In an important milestone, the Webkit team announced that they passed this final hurdle. Congratulations to all the people that made this possible! With the Chrome browser also using the Webkit engine, there will soon be at least two browsers that fully pass this test. Even though it’s not proof that they conform to all current standards, these tests contain some pretty tough cases.
For an overview of how other browsers are doing see this wikipedia article; most notably, IE7 scores 14 points, the latest IE8 beta is at 21 and the development builds of Firefox are at 89%.