Is IE9 a modern browser? NO, says Mozilla. IE9 is definitely better than IE8 and a step in the right direction, but it cannot be called a truly modern browser, says Paul Rouget of Mozilla, in a blog post.
Does IE9 support 99% of the HTML5 specification as insinuated by Microsoft? No, they’re actually pretty far from it. The tests Microsoft are referring to are the ones they created during the development of IE9. It’s not that surprising that they pass the very tests they used to design and develop the browser – we score pretty well against our own unit-tests as well. The primary use case for these tests, however, is to spot regressions and validate code changes. In other words: the tests ensure that future changes don’t break the things you just built. They don’t actually test all elements of a specific standard.
The blog post at Mozilla.com even goes on to say that IE9 is 2 years late!
Microsoft had earlier made a blog post suggesting that the new IE9 offered more extensive HTML5 support and other features compared to other browsers.