The Mozilla Foundation has started work on a Firefox port that will run in the Windows 8 classic desktop and the tablet-friendly Metro user interfaces.
Moz dev Brian Bondy, who described the project in detail on his blog, said the goal is to deliver a single browser capable of straddling the Microsoft operating system's split personalities, rather than building two separate applications.
Mozilla unveiled its plans for Firefox on Windows 8 in February. An alpha and beta are due in the second half of 2012.
The unified build of Firefox will be a "Metro-style enabled desktop browser", allowing it to compete directly against Internet Explorer 10. This is a third application type; until now the assumption had been there would be just two operating modes for Windows 8 programs: classic desktop or Metro.
"Provid[ing] HTML5 rendering for webpages and service HTTP/HTTPS requests. By definition, such a browser has 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)."
IE10 - the default browser for Windows 8 and both released as Consumer Previews at the end of February - is such a "Metro-style enabled desktop browser" according to Microsoft.
For this project Mozilla will craft a Firefox browser with the same system-level parity as IE10, built using traditional Win32 calls and the new Windows Runtime WinRT, the framework for Windows 8 Metro apps.
Dotzler wrote: "We should be able to build a single product, that when installed into the Classic environment via traditional means - a download from www.mozilla.org - will be able to become both the default browser in the Classic environment and in the new Metro environment. We'll, of course, have a Metro-specific front-end that fits in with the new environment, but we will not have to deploy two completely different browsers."
Two questions remain: one is whether or not Microsoft will actually permit rival software into the Windows 8 store that can be set as the default browser and elbow IE10 aside.
The other is whether or not Mozilla's work will easily transfer to Windows on ARM, about which Microsoft has said very little and for which a Windows 8 Consumer Preview is not available. Dotzler does note, however: "Microsoft had an awful big head start with IE 10 but now that we know what's possible, we hope to close that gap."
Of course, Firefox could go on to beat IE10. As El Reg regular Tim Anderson pointed out here, IE10 on Windows 8 has not successfully straddled the two worlds of classic and Metro. Pages open in IE10 in Metro are not visible in IE10 on the classic desktop, and vice versa, and cookies are not shared. This is more than just a basic oversight - it'll be confusing for users.
"If we do our job, Firefox on Windows 8 Metro should be every bit as capable and integrated with the system as Internet Explorer," Dotzer said. In light of Anderson's comments, let's hope more so. ®