Mozilla has taken another step toward delivering a "Metro" version of Firefox to Windows 8 users.

Late Tuesday, Asa Dotzler, the Firefox desktop product manager, announced that a preliminary Metro browser had reached "mozilla-central," the source code repository that feeds into what Mozilla calls the "Nightly" build channel.

Nightly builds are designed for testing, and as the name implies, are automatically updated each night to that day's edition. Firefox's Nightly builds are Mozilla's roughest-edged editions. Every six weeks, the current Nightly morphs into an Aurora build -- analogous to an alpha -- that kicks off a three-month development cycle which ends when the next iteration is officially released.

"If you are on the Firefox Nightly channel and you have a Windows 8 device, your Wednesday Firefox update should deliver a Metro Firefox tile to the far right end of your Windows Start screen," Dotzler wrote.

Like many, Dotzler used "Metro" to refer to the kind of apps that run in the new tile-based user interface (UI) of Windows 8, even though Microsoft abandoned the label last summer.

"There's plenty of work still to do, but it's stable enough that we're ready for more and more regular testing," added Dotzler.