Mozilla plans to redesign the graphical user interface of future versions of its open source browser for the Windows operating system. In this regard, the initial themes for revamping Windows is already published, and available via Mozilla Wiki. According to Mozilla, the GUI overhaul is planned for Firefox version 3.7. At this point in time, users can download Firefox 3.5, which has been made available at the end of June, 2009. The mockups involve the GUI on the various releases of the Windows client, including Windows 7, Windows Vista and Windows XP.
More info: Windows Theme Mockups for Firefox 3.7