Firefox 3: Preview of the User Interface
It uses version 1.9 of the Gecko rendering engine–which itself hasn't been released yet and which includes the Cairo graphics layer.
There are also a wide range of improvements to performance, stability, and security, and it's also going to present several new user facing features.
Here is a quick recap of design work that's been going on in the Mozilla community over the past few weeks for Firefox 3.
Places: Bookmarking, Tagging and History
Places is our new infrastructure for storing bookmarks, history, and other information about Web pages. The current implementation of the Places system is still a work in progress, but the final version will support features like bookmark tagging, full-text indexing, extended metadata search, built-in syncing functionality, and support for exporting bookmarks in a broader number of formats.