Has it really been this long? Mozilla started to work on the Metro version of the efox web browser back in 2012 before Microsoft released the retail version of the successor of Windows 7 to the public.
Windows 8 introduced a then-called Metro interface to the Windows operating system that was heavily optimized for touch displays.
Legacy programs would not run on the Start Screen interface, and while x64 and x86 Windows 8 users could run them on the desktop part, users of Windows RT could not.
Microsoft shipped the operating system with custom versions of core Windows programs such as Internet Explorer, and new apps that it created just for the operating system.
Third-party Windows developers had two choices now. They could either create a specialized version of their program for the Start Screen interface, or ignore it completely.
Mozilla's attempt to create a version of Firefox for Windows 8 was plagued by development issues and delays, and while progress was made, the organization never released a stable version of Firefox for Metro.
Today, Mozilla announced that it made the decision to pull the Metro version of the Firefox browser. What this means that the project is dead, at least for now.
One of the main reason for the decision are low user numbers in comparison to desktop beta builds of Firefox. Mozilla states that no more than 1000 users used Firefox for Metro actively daily.
While that can be partially attributed to the non-existent marketing to promote the app version of Firefox to the community, it is more likely that the core reason is that there are not many use cases where users would select to use the app version over the desktop version.
Touch users on Windows 8 are probably the main target audience for an app version of the browser. Even if the Metro version would have all the features of the desktop version -- which it did not at any time -- it is fair to say that most users would have picked the desktop version of Firefox instead.
With Firefox for Metro gone, Mozilla will concentrate its resources where the organization can reach more people.