* Star button: quickly add bookmarks from the location bar with a single click; a second click lets you file and tag them.
* Tags: associate keywords with your bookmarks to sort them by topic.
* Location bar & auto-complete: type the title or tag of a page in the location bar to quickly find the site you were looking for in your history; favicons, bookmark, and tag indicators help you see where results are coming from.
* Smart Places Folder: quickly access your recently bookmarked and tagged pages, as well as your more frequently visited pages with the new smart places folder on your bookmark toolbar.
* Bookmarks and History Organizer: advanced search of your history and bookmarks with multiple views and smart folders to store your frequent searches.
* Web-based protocol handlers: web applications, such as your favorite webmail provider, can now be used instead of desktop applications for handling mailto: links from other sites. Similar support is available for other protocols (Web applications will have to first enable this by registering as handlers with Firefox).
* Easy to use Download Actions: a new Applications preferences pane provides a better UI for configuring handlers for various file types and protocol schemes.
The production version is due some time soon, so watch out for announcements.