Why Internet Explorer 8 might not pass the Acid2 test
Unperturbed, we tried again later, and the second time was a charm. IE8 passed the Acid2 test with flying colors. So what was the difference between attempt 1 and attempt 2?
The second time, we went to the official Acid2 test page. The first time we had gone to another site that was hosting a copy of the original test. While you'd think that a web browser that's capable of rendering one page properly should be able to handle the same content on another page, the folks at Microsoft's IEBlog point out that IE8 performs a cross-domain security check for ActiveX controls which will prevent it from passing the Acid2 test on any page but the official one.
So there you go, Internet Explorer 8 is standards compliant. Under the right circumstances.