Which browser version was the first officially released browser to pass Acid2?

The first officially released browser to pass Acid2 was Safari 2.0.2.

Acid2 was released in April 2005 by the Web Standards Project to test browser support for parts of HTML, CSS 2.1, PNG images, and data URIs. A successful browser renders a distinctive smiling face, including the correct layout, colors, and blue nose when the pointer is placed over it.

Safari achieved a pass in a private build in April 2005, before the result became part of a public release. Safari 2.0.2, released on October 31, 2005 and included with Mac OS X 10.4.3, was therefore the first officially released browser credited with passing the test. That distinction matters: several browsers, including development builds of Safari and others, passed earlier.

Opera, Konqueror, Firefox, and Internet Explorer later followed. Firefox 3.0 passed Acid2 in 2008, while Internet Explorer 8 became a major milestone in 2009. Acid2 tested rendering standards rather than overall browser quality, so passing it did not mean every web-compatibility problem was solved.