Mozilla announced in early 2012 that they will be developing a Modern UI version of Firefox on Windows 8. After almost two years since the announcement, the product is now scheduled to be released to the general public in March 2014. Earlier it was planned to include this new modern version with the release of Firefox 27, but it is now delayed to release it with Firefox 28.
Mozilla still feels that they are few bugs to be fixed before it can released to the general public. Currently, Internet Explorer is the only browser that Windows 8 ModernUI users can enjoy. And this situation will soon change with the release of Firefox for Modern UI.