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.