We used "Firefox for Metro" only as a code name for the project; it doesn't appear in user-facing strings in the product.

We've been using that project name for a couple of years, and haven't seen a good reason to change. Microsoft hasn't settled on a useable replacement. For a while they used "Modern style" but now they've dropped that too. Now they mostly use "Windows Store app" in their developer documentation, but we found that too confusing, especially since Metro-enabled desktop browsers like Firefox and Chrome aren't necessarily installed through the Windows Store. Meanwhile, the Microsoft white paper on "Developing a Metro-enabled desktop browser" was retitled "Developing a new experience enabled desktop browser" [1], which is even less... wieldy.

[1] http://msdn.microsoft.com/en-us/library/windows/apps/hh46541...

Because "the artist formerly known as Metro" was too long.