This is a must-know for those who love some old extensions that are no longer compatible with their new upgrade of gnome shell, since many extensions are already compatible with the new versions of the gnome-shell, but all what differs is that this is not explicitly stated in the meta-data file.

My system is on Ubuntu 13.04 beta with Gnome 3.8.

Here are the steps:

1. Get the exact version of your gnome-shell, “gnome-shell –version”, mine is 3.8.0.1
2. Download the 2 files of any extension, extension.js and metadata.json, or simply copy their text into new empty files that you create (with the same name of course)
3. In the .json file, go to the shell-version section and your version that you got into step 1, e.g.: “shell-version”: [
        “3.2”, “3.5.2”, “3.8.0”, “3.8”, “3.8.0.1”
     ],
4. From the same file, you will find a uuid section, you will use that name to create a folder with the same name, e.g. folder name would be steal-my-focus@kagesenshi.org in this example: “uuid”: “steal-my-focus@kagesenshi.org”
5. Copy the two files into that folder
6. Copy that folder into “~/.local/share/gnome-shell/extensions
7. Restart your shell, you can do that by pressing Alt+F2 then typing r and pressing enter
8. Go to your gnome-tweak tool and activate that new extension by setting to on or activate it through the web interface
9. Enjoy!