What will Firefox and Chrome bring to Windows 8 Metro?

As Mozilla and Google build Metro-style browsers for Windows 8, a loophole in Microsoft's spec may let them sidestep ban on add-ins -- including Flash

There was never any doubt Firefox and Chrome would come to the Windows 8 Metro Start screen. Both Firefox and Chrome work fine with the Windows 8 Consumer Preview legacy desktop. We haven't seen Metro versions yet, but they're on their way.

Firefox's Brian Bondy confirmed late last week that work has already begun on a Metro-style version of Firefox. Yesterday a Google spokesperson confirmed to Mashable that Chrome, too, is coming to the Metro Start menu. Neither the folks at Opera nor Safari's handlers at Apple have made it official yet, but it seems inevitable that they'll also put on a touch-friendly face. All of this is made possible by an open invitation from Microsoft for developers to hook together Metro-style and legacy desktop versions of their browsers.

But Metro has a "no add-in" restriction for Metro browsers, which by default bars Flash. There's a loophole in the spec, though, that has me wondering whether some smart browser programmers will find a way around it.

Microsoft published a white paper a couple of weeks ago that includes ground rules for "Developing a Metro style enabled Desktop Browser." Browsers occupy a unique gray area in the Windows 8 milieu: They "may be designed to access both the Metro style experience as well as the traditional desktop experience." Although the Metro side of the browser runs in the now-familiar full screen Metro "immersive" part of Windows 8, the browser is also granted "full access to Win32 APIs for rendering HTML5, including the ability to use multiple background processes, JIT compiling, and other distinctly browser-related functionality (like background downloading of files)."

No other apps in Windows 8 are allowed to straddle the Metro-legacy desktop fence like that. The pairing of Metro-style and legacy desktop browsers may open up a whole world of interesting possibilities. What's to keep a little Metro-style browser from calling its big legacy desktop twin and handing off the dirty work -- the stuff that requires add-ins -- to the desktop version?

Apparently Microsoft put that loophole into Windows 8 so that the legacy desktop version of IE10 can render HTML5 and service HTTP requests for the Metro version of IE10. What's good for the goose is good for the gander, and Microsoft is now permitting other browsers to jump the fence in the same way.

I've read the white paper over and over, and for the life of me I don't see any wording that makes it technologically impossible for a Metro browser to request, say, a Flash file from the desktop side and have the desktop side retrieve and render the Flash file. The only restriction I see is that the video would be passed back over the fence in HTML5 format.

There's some talk in the white paper about restrictions on input threads headed to the desktop and Metro parts of the browser, but that doesn't appear (to me, anyway) to preclude running an add-on.

Yes, I'm saying that this white paper seems to open the door for Metro browsers to play Flash files -- or, say, for Metro IE10 to ask its legacy desktop cousin to run ActiveX controls.

Brian Bondy on the Firefox Metro team has already documented a pile of problems with the white paper. Perhaps this is something that just fell through the cracks. But it does open up a tantalizing possibility.

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