Following are common features of Firefox 4.0:
The new, sleeker, updated interface lets you use your browser more conveniently. Moreover, new features like App Tabs and Panorama make it easier to browse the web.
Firefox Sync lets you synchronize your settings, passwords, bookmarks, history, open tabs, and other customizations across multiple devices (mobile and PC) so you can take Firefox with you wherever you go.
The new privacy feature ‘Do Not Track’ helps you keep your privacy online. It blocks advertisements that track your behavior online. You can read more about here.
Download Firefox 4.0 at Mozilla here.