If you are using an up-to-date installation of Debian Testing today, you have probably realised that Gnome-Shell is only available in version 3.0 from the testing repository at the time I'm writing this article (21.01.2012).

Introduction

If you want to install some extensions to make Gnome more usable, you will need a version of Gnome-Shell <= 3.2.
You can track the Status of Gnome 3.2 in Debian from this page.
As you can see, the Gnome-Shell 3.2 package is stuck in the Unstable repository for some reasons which means we will have to install it directly from Unstable.

Disclaimer

You understand that we are going to install a package from the Unstable repository (also called SID for Still In Development) so please don't blame me if something goes wrong :-)

Installation

Open a terminal and login your root account or use sudo before typing the following commands.

First, make sure you system is up-to-date:

# apt-get update && apt-get upgrade

Open your sources.list in order to add the Unstable repository (sid):

# nano /etc/apt/sources.list

Then paste the following lines:

##DEBIAN SID
deb http://ftp.debian.org/debian/ sid main non-free contrib
##deb-src http://ftp.debian.org/debian/ sid main non-free contrib

Once this is done, you can save and close the file but you will need to reload the package list:

# apt-get update

Then you can install Gnome-Shell from the sid repository:

# apt-get install gnome-shell/unstable

When the install of Gnome-Shell is finished, I recommend you remove (or comment) the lines we added to the sources.list file.

Conclusion

That's it. You can now install extensions from your broswer (you will need to use a compatible browser such as Firefox Iceweasel or Epiphany) and start enjoying the other great features of Gnome 3.2.