* Integration with Windows: Firefox now has improved Windows icons, and uses native user interface widgets in the browser and in web forms.
* Integration with the Mac: the new Firefox theme makes toolbars, icons, and other user interface elements look like a native OS X application. Firefox also uses OS X widgets and supports Growl for notifications of completed downloads and available updates. A combined back and forward control make it even easier to move between web pages.
* Integration with Linux: Firefox's default icons, buttons, and menu styles now use the native GTK theme.
* Places Organizer: view, organize and search through all of your bookmarks, tags, and browsing history with multiple views and smart folders to store your frequent searches. Create and restore full backups whenever you want.
Edit: A lot of the add-ons need to be updated to work in the new beta.