Compatibility

When it comes to supporting new Web standards, IE9 is on the right track. Microsoft has moved more deliberately than other browser makers, often submitting cases to the World Wide Web Consortium before implementing a feature. Support for HTML5, CSS3, Canvas, location services, and SVG has made its way into Microsoft's browser, but IE9 still trails Chrome in sheer number of supported emerging Web features.

On the widely cited Acid3 test of adherence to Web standards, IE9 is up to 95 out of a possible 100—remarkable for a browser stuck in the 20s for years—but unchanged from the beta. Microsoft has stated that implementing some Acid3 features would constitute a security risk. It's also worth noting that the Web Standards Project that puts out the test isn't an official standards body, and many have claimed it's an arbitrary set of requirements. Still, it's an interesting metric.

More granular is the HTML5Test, which shows how many HTML5 elements and features a browser supports out of 400. It also notes "bonus" points for features that aren't required parts of HTML5, but are good to have, such as extra video codecs. On this test, Chrome leads all other released browsers, with a score of 288 and 13 bonus points. IE9 ups its game from 96 and 3 bonus points in the beta to 130 and 5, but it still trails most other new browsers.
Browser HTML5Test.com Score (higher is better) Bonus Points
Google Chrome 10 288 13
Firefox 4 RC 240 9
Opera 11 177 7
Safari 5 165 0
Firefox 3.6 139 4
Internet Explorer 9 130 5
Internet Explorer 8 27 0

A truly valid test will be available when the W3C finishes its HTML5 Test Suite, but as of this writing, the organization cautions against quoting that. IE9, so far, is among the top in the test's results, and the site gives an eye-opening look at how much is involved in implementing the new standard.

In real-world site compatibility testing, I found that IE9 worked perfectly in far more sites than the beta did—you have to look high and low to find one that doesn't display correctly. I had no trouble signing into my Citibank, Fidelity, and Omniture accounts. Even our Vignette CMA, which has trouble in just about every browser except IE7, again works perfectly in IE9. But in the new Yahoo Mail site, the built-in slideshow viewer didn't display. There will always be some sites that choke any browser, and this was likely a result of IE9 still being new.