OperaWatch reports that this week’s development build of Opera passes the Acid2 test. This makes Opera the first browser for Windows to pass! Previous browsers included Safari (Mac only), iCab (Mac only), and Konqueror (Linux/Unix). I’m sure you could get Konqueror to run on Windows under Cygwin, but it seems like a lot of effort just to run a web browser.
Opera cautioned that upcoming development builds could regress, but we can expect the final version of Opera 9 to pass the test.
Neither Internet Explorer 7 nor Firefox 2 will make any attempt to pass Acid2, but Mozilla is working on Acid2 fixes in the next version of their rendering engine, Gecko 1.9, which will likely appear in Firefox 3.