http://www.youtube.com/watch?v=HmgtW2Iw-kE&feature=player_embedded
If you're the type to live life on the edge, Mozilla has just posted the Firefox 4 Beta 1 candidate build. The early version has many of the upcoming features we've heard about, including a new menu button that aggregates the most frequently used browser menu options, native compatibility with Windows Vista and 7's Aero Glass interface, a customizable tab bar, and a bookmarks button.
Firefox 4 Beta 1 candidate also relocates the default position of tabs to above the address bar – a move many users claim Mozilla is copying from Chrome and Opera. The organization wants you to know that isn't the case. To set the record straight, Mozilla has released a video explaining the thought behind shifting the tabs northward, and the reasoning seems logical enough.
http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/4.0b1-candidates/build1/win32/en-US/