Just in time for some last-minute testing, Mozilla has released the first preview of its Firefox Web browser built for Windows 8's 'Modern UI' interface. Admittedly, 'Modern UI' doesn't quite roll off the tongue like 'Metro', so Mozilla has decided to stick with the term despite Microsoft's opposition to it.
'Firefox Metro Preview' can be installed to Windows 8 using the latest development package grabbed from the Elm development folder (for most, the installer.exe file will be most suitable). After the install, Firefox will need to be made the default browser. If it's not, clicking the icon inside of the Start screen will simply bring you to the desktop variant of the browser. In personal tests, it seems that all Web browsers under Windows 8 work like this, which is a little unfortunate.
As the screenshot can attest, this version of Firefox will feel familiar to anyone who's used a recent version of the browser on either iOS or Android. Tabs are located up top, and the on-screen buttons are kept to a minimum. The entire area underneath the address bar is dedicated to content, and overall I have to say it looks quite nice. This design is the reason I tend to be drawn more to Firefox on Android than any other browser.
One major change this particular version of Firefox does have, though, is a tweaked start page to better fit in with Windows 8 styling. Bookmarks are stored as colored tiles (which draw their color from the emoticon), while the recent history can be found to the immediate right. This browser, unlike Microsoft's built-in Internet Explorer, supports Sync, and past that, also supports swipe gestures and has integration with Start's "Charms" feature (essentially allowing you to search within the Start page but show the results in Firefox).
Unfortunately, I haven't had any success getting this build to work, although I'm not running the official RTM build (rather, the 90-day trial) and am also running it inside of a virtual machine. While it seems unlikely that either of these factors matter, it's really hard to know for sure. In perusing the Web, I can tell I'm not the only one who thinks Mozilla's first Metro-based release here is buggy, however, so it does seem to need a lot more TLC before it launches as a final version.