An about-face in Internet Explorer 10 shows Microsoft is not merely backing off from its hostility toward Flash Player, but actually warming up to the Adobe Systems browser plug-in for competitive reasons.

In September 2011, Microsoft declared that browser plug-ins are a relic from the Internet's early days, calling them bad for battery life, security, reliability, and privacy, and said that it would ban them when IE10 was running with Windows 8's Metro user interface, now called the "immersive UI."

But Microsoft gave Flash a reprieve in May 2012 by building a special version of Adobe's plug-in directly into IE10. It only worked, though, on sites that were specifically authorized through a Microsoft whitelist when browsing with the immersive UI on Windows 8 and on either the immersive or traditional "desktop" interface on Windows RT.

Yesterday, Microsoft loosened its Flash policy again, this time enabling Flash by default on both Windows 8 and Windows RT. Now, instead of using a whitelist to enable Flash only where Microsoft permitted it, the company now uses a blacklist to block Flash "in the small number of sites that are still incompatible with the Windows experience for touch or that depend on other plug-ins," said Rob Mauceri, program manager of Microsoft's Internet Explorer group, in a blog post yesterday. (The new policy doesn't change Microsoft's Flash-permissive stance with IE10 in desktop mode on Windows 8, which always has permitted Flash.)

For years, Flash was the preferred way for programmers to bring interactivity, animation, video, and other advanced features to the Web, but Adobe canceled its effort to bring Flash to mobile devices after Apple barred it. Adobe has since redirected much of its engineering work to re-implementing many Flash abilities with Web standards such as HTML and CSS. Flash remains widely used on the Web, and likely won't be replaced on older sites that no longer are maintained.

Mauceri apparently sees Windows' Flash support now as a competitive advantage in the company's push to spread Windows beyond PCs to tablets, too. Flash is effectively dead for Android and iOS tablets, but Microsoft sees a role for it, Mauceri said:

We believe having more sites "just work" in IE10 improves the experience for consumers, businesses, and developers. As a practical matter, the primary device you walk around with should give you access to all the Web content on the sites you rely on. Otherwise, the device is just a companion to a PC... IE10 with Flash on Windows 8 enables people to see more of the Web working with high quality, especially compared with the experience in other touch-first or tablet browsers and devices.

That language recalls to mind one early aspect of the Android sales pitch -- that Android devices work better than iOS devices because Flash support gives browsers access to the "full Web." That marketing line died when Adobe scrapped its effort to build and promote Flash for mobile devices.

Microsoft watcher and ZDnet blogger Ed Bott sees the change to permit Flash as pragmatic. "For Windows RT in particular, it had a devastating effect on some sites, which simply wouldn't work, and the fact that you can't install an alternative browser on RT eliminates that workaround. And at this point in its life, the last thing Windows RT needs is another reason for potential buyers to reject it," Bott said.

Some of Microsoft's change of heart came through Adobe's work to improve Flash itself:

For Windows 8, we worked with Adobe to include a version of Flash that is optimized for touch, performance, security, reliability, and battery life. Adobe made substantial changes to the Flash player to align with the Windows 8 experience goals. We shipped this optimized Flash component as part of Windows 8, and we service it through Windows Update.

The moves help improve Flash's fortunes, but only modestly. Microsoft and Adobe both are working to advance programming using Web standards rather than plug-ins, and major allies include Mozilla, Google, and Apple share that agenda. The cross-platform advantages of Flash programming are undermined significantly when it can't reach some platforms. Flash will never be eradicated from the Web, but with each passing year there's less and less need for it.