When we say Firefox will be going Metro, we are not talking about its sexuality. In fact, we are referring to the new Metro interface which will be implemented as a part of Windows 8 to further its goals of introducing a uniform touch UI across PCs and smart devices.
PC version of Windows 8 will feature a Classic user interface as well, but it is expected that Windows 8 tablets will have very limited standard OS features. The tablet and smart device sector has been one area of major growth for browsers and Mozilla cannot afford to neglect this segment.
Hence, besides the standard Firefox browsers available, Mozilla will be introducing a version that maximizes on the potential of Metro. The new Firefox for Windows 8 will still be a Gecko-based browser, but it will support touch interactions. Mozilla may also possibly include live tiles as a feature. However details cannot be confirmed until the Consumer Preview of Windows 8 is released so that concepts can be implemented and tested.
A complete roadmap of Mozilla's plans for the development of its Firefox browser with respect to Metro has been released. Hoepfully a smart and innovative implementation of live tiles is part of the final product. We can see Microsoft's dogged pursuit of a unifying OS across all modern devices is beginning to affect third parties. While Mozilla has somewhat revealed their hand, other browsers have yet to release information.