Mozilla has unveiled its first public preview of how Firefox will look when run using Windows 8’s new tile-based interface. Firefox Metro UI Preview is based on an offshoot Nightly build of Firefox, codenamed “Elm”, and can be downloaded and tested now on PCs running Windows 8.

This early preview provides a fully functional web browser, complete with multi-touch support on compatible displays. However, as expected at such an early stage in its development, not all planned features have yet been implemented, while the Nightly tag indicates this is a largely untested build.

Once downloaded, users should install Firefox Metro UI Preview using the standard options. As a Nightly build, Firefox Metro UI Preview will install alongside non-Nightly builds of Firefox such as Firefox FINAL and Firefox Aurora, although it will overwrite any other Nightly build installed.

The first public preview of how Firefox will look as a full-screen Windows 8 app has been released.

Once installed, launch Firefox Metro UI Preview from the desktop or Start screen, and it will prompt you to make it the default browser – do so, and then assign any default actions to it when prompted. Close the browser, then switch to the Start screen. You’ll now see the Firefox nightly icon has been replaced with a dedicated tile – tapping this launches Firefox Metro UI Preview in all its glory.

As expected, the browser uses a full-screen approach, with tabs and a control bar accessible from the top and bottom of the screen respectively. With documentation thin on the ground, it will take some time to navigate the program, but we were able to glean that swiping down from a narrow area in the top left corner made it possible to permanently view thumbnail previews of all available tabs. From here, clicking … revealed an option to permanently pin the tabs themselves to the top of the screen for easy access.

At this early stage, Firefox Metro UI Preview is clearly not ready for mainstream use, with features missing and not working as expected. However, it does provide a full-screen web browsing experience, and while much work is to be done before it can be integrated into the main Nightly build ahead of its long road to final release, it’s clear that Mozilla is making good progress in delivering on its promise of an alternative tile-based browser to Internet Explorer.

Firefox Metro UI Preview is available now as a free open-source download for PCs running Windows 8. As this is untested and unstable software, users should take a backup of their system before proceeding.