TwentyTen is a beautiful theme for Firefox based on the style of Microsoft Office 2010, but also with a touch of the upcoming Firefox 4.0 design.

This theme is customizable through TwentyTenBuddy, a Firefox extension that is installed toghether with TwentyTen. This extension allows you to choose among 9 different colors and set some options, such as enable or disable the Aero Glass effect on Windows Vista o Windows 7, show or hide the new tab button and the tab close bottom, etc.

Moreover, the theme supports Fission extension, an addon that gives more visibility to the progress bar by putting it on the address bar, and with Aero Glass activated looks really nice on TwentyTen.