After two years of struggling to build a hybrid Firefox for Windows 8, Mozilla has finally thrown in the towel.

Firefox Vice President Johnathan Nightingale made the announcement today in a post titled “Metro,” on Mozilla’s Future releases blog.

Earlier this week, I asked our engineering leads and release managers to take the Windows Metro version of Firefox off the trains. The team is solid and did good work, but shipping a 1.0 version, given the broader context we see for the Metro platform, would be a mistake.

The decision means that Firefox will continue to be developed for the Windows desktop platform without the significant burden of building an additional version that would use the same rendering engine but run in the touch-friendly but significantly more constrained Windows Store (née Metro) environment, alongside other Windows 8 native apps.

The project had nine dedicated engineers and two product managers listed in its 29-person team roster. It took nearly a year after the first appearance of a Metro style Firefox prototype in April 2012 before the Metro code made it into the Nightly channel . Last summer, the team had declared its intention to ship the final Metro code with Firefox 26 on December 10, 2013. In January, that final date slipped to March. Today’s announcement ends all development.

According to Nightingale, the failure of Firefox Metro follows a familiar story line: overly optimistic early expectations followed by disappointing adoption rates.

In late 2012, when I started up the Firefox for Metro team (I know that’s not what Microsoft calls it anymore, but it remains how we talk about it in Mozilla), it looked like the next battleground for the Web. Windows is a massive ecosystem and Microsoft pushes its new platforms hard. […] [A]s the team built and tested and refined the product, we’ve been watching Metro’s adoption. From what we can see, it’s pretty flat. On any given day we have, for instance, millions of people testing pre-release versions of Firefox desktop, but we’ve never seen more than 1000 active daily users in the Metro environment.

Part of the cause of that low usage rate is simply a case of too few touch-enabled devices running Windows 8. Every x86-based PC that runs any version of Windows, from XP through Windows 8.1, can run the desktop version of Firefox. The pool of devices capable of benefiting from a touch-optimized Metro Firefox is much smaller, perhaps one-thirtieth of the larger population.

Even more damning for the future of Metro Firefox was the lack of a compelling competitive case against Internet Explorer 11, the touch-enabled browser that’s included with Windows 8.1. Firefox made its reputation a decade ago as an alternative to IE 6—faster, less plagued by security concerns, and more in tune with emerging HTML standards. But in the Metro platform, Microsoft held all the advantages, with a fast native browser, a no-plugins model that blocks toolbars and most malware, and a significant head start in development. In fact, Microsoft is about to ship a major update to Internet Explorer next month with Windows 8.1 Update 1 . That will be its second major refresh since the original IE 10 release in Windows 8.

Mozilla’s architects didn’t help their cause by creating a program that forces users to choose between desktop and Metro modes instead of allowing both modes to operate side by side as IE does.

Google, for its part, will continue to include a bare-bones Metro version in its shipping code for the Chrome browser. But it’s become clear that Google has no intention of building any products except a Google Search app for the Metro environment.

And with Mozilla's exit, that leaves Microsoft all alone in the Metro browser development business.