Built in Phishing Protection.
Search suggestions now appear with search history in the search box for Google, Yahoo! and Answers.com
Changes to tabbed browsing behavior
Ability to re-open accidentally closed tabs
Better support for previewing and subscribing to web feeds
Inline spell checking in text boxes
Search plugin manager for removing and re-ordering search engines
New microsummaries feature for bookmarks
Automatic restoration of your browsing session if there is a crash
New combined and improved Add-Ons manager for extensions and themes
New Windows installer based on Nullsoft Scriptable Install System
Support for JavaScript 1.7
Support for client-side session and persistent storage
Extended search plugin format
Updates to the extension system to provide enhanced security and to allow for easier localization of extensions
Support for SVG text using svg:textPath