Mozilla developers are planning to build a dramatically different version of Firefox for Windows 8, a change necessitated by Microsoft's use of the touch-friendly "Metro" user interface for PCs and tablets.

Mozilla describes its Windows 8 plans as part of a 2012 Strategy & Roadmap document updated yesterday. A technology proof-of-concept demonstrating the feasibility of Firefox in Windows 8 is planned for the second quarter of this year, with timing dependent on the release of Microsoft's Windows 8 consumer preview and developer documentation. A Metro version may be necessary for Firefox to avoid being shut out of Windows 8 tablets running on ARM, which will have only a limited "traditional" Windows desktop. But Mozilla is apparently planning Firefox builds both for the traditional Windows desktop environment and Metro.

"Windows 8 contains two application environments, 'Classic' and 'Metro,'" Mozilla notes. "Classic is very similar to the Windows 7 environment at this time, it requires a simple evolution of the current Firefox Windows product. Metro is an entirely new environment and requires a new Firefox front end and system integration points."

Metro Firefox will be a new Gecko-based browser focused on touch interactions, with both full-screen and partial-screen modes, with the possibility of a live tile so that users can see updates on the Start screen. There are several unanswered questions, such as which programming language to use for building the Metro front end. Firefox product manager Asa Dotzler further notes that "This proposal depends on Microsoft providing the same capabilities for Firefox as it does for IE—running at the Medium level integrity process that allows us the full use of the Win32 API and what we need from Metro, or a set of APIs that allow Mozilla to port Gecko to the WinRT. For the purposes of this feature proposal, I'm assuming we'll get the first and we won't have to port the bulk of Gecko and instead will use the win32 dlls from within Metro."

Firefox accounts for about 20 percent of worldwide desktop browser market share, but has lost ground to Google Chrome over the past year. Chrome will presumably have a Metro version for Windows 8 as well, but Google has made no official announcement.