Browser wars never end and Acid2 test is considered the ultimate yardstick for web standard compliance.
Here is some history and background of Acid2 test from wikipedia:

Acid2 is a test suite published and promoted by the Web Standards Project to identify web page rendering flaws in browsers and authoring tools. Acid2 was released on April 12, 2005. It has been developed in the spirit of the Acid1 test from 1998. The Acid tests test many features on a single page and report test results graphically.

Acid2 tests features of HTML and, more prominently, CSS. The purpose of testing such features is to highlight the problems with browsers that do not display it correctly. The Acid2 test should render correctly on any browser that follows the W3C HTML and CSS 2.0 specifications. Because Acid2 tests how web browsers deal with faulty code, the test is intentionally not written to W3C CSS standard specifications, and fails validation. This is expected and was the intention of its designers.

Let’s test out the leading browsers and see how they handle Acid2 test, including the latest IE8 beta .

(click on images to get larger size)

IE7:

IE8:

Firefox2:

Safari:

Opera:

Netscape:

Safari and Opera are the only browsers that seem to pass the Acid2 test. IE8 is very close but not quite there.