The latest Firefox 3.7 Alpha 4 Preview build supports Aero Glass under Windows Vista and 7. Now it looks very close to the thing which was shown in earlier mockup themes.
http://ftp.mozilla.org/pub/mozilla....nk/firefox-3.7a4pre.en-US.win32.installer.exe
http://ftp.mozilla.org/pub/mozilla....nk/firefox-3.7a4pre.en-US.win32.installer.exe