Mozilla released second beta version of Firefox 4 which comes with a new page building mechanism, improved speed, and support for CSS Transitions.
One of the main feature of Firefox 4 beta 2 is, it has included tabs on top interface for Mac OS X users that Mozilla gave Windows users as the default interface in Beta 1.It also provides users to change regular tabs into more compact tabs that cannot be deleted accidentally.
So now you can create an app tab for any site by right-clicking on the tab and selecting “create App Tab.” Another new feature is the beta includes a new Feedback Add-on , when you can click the Feedback button , it gathers your likes or dislikes about Firefox. The Firefox 4 beta 2 is available for Linux, Mac and Windows PCs, you can download it over here.
Check out blow video which demos how Tab Apps work :
To know more about the features of Firefox 4 Beta 2, check out Mozilla blog