New in Firefox 4:
- The “pin as app tab” feature minimizes frequently used pages into a favicon -only tab for easy access.
- Consolidated menu bars give the site more space and reduce the space taken by navigation.
- A completely customizable interface that allows you to add and remove buttons, bars and more in any way you like.
- The "tab group" feature gives you the ability to group tabs together without opening a new window, which is useful for placing similar sites in groups and keeping track of multiple projects.