Check Deb Richardson's site where she is written a detailed guide for the Firefox 3 users. This is simply amazing.

• Add-on manager
• Bookmarks
• Cascading Style Sheets (CSS)
• Color profile support
• Download manager
• Font and text rendering
• Full page zoom
• History
• HTML Canvas
• Location bar UTF-8 support
• Malware protection
• Microformats API
• Offline web application support
• Password manager
• Performance improvements
• Phishing protection
• Plugins
• Site Identification button
• Smart Location Bar
• Tabs
• Themes
• Video and audio feeds
• Vista parental controls support
• Web application protocol handlers
• Conclusion

It is here, check it out