Flock the social networking based fork of Mozilla has a much better interface than Firefox, if you are looking to get the same interface to Firefox, you are in luck.
A new experimental theme has been released for Firefox which is based on Flock. The theme looks pretty decent and similar to Flock.
Installing this theme will not bring the social networking features to Firefox, to do that you can check our earlier post: Converting Firefox into a Social Networking Hub.
The theme is compatible with Firefox 3.5.1 and earlier versions.