Firefox  4.0 Beta 2
- Tabs are now on top by default on Windows and OSX - Linux will be changing when the theme has been modified to support the change.
- You can turn any tab into an "App Tab" by right-clicking on it and selecting "Make into App Tab" from the context menu.
- Web developers can animate content using CSS Transitions.
- Responsiveness and scrolling improvements from the new retained layers layout system.
- Changes to how XPCOM components are registered in order to help startup time and process separation.