Cannot install gnome extensions from GNOME site

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http://askubuntu.com – I have installed Ubuntu 12.04 and installed gnome-shell on my system. I am attempting to download the user theme extensions from extensions.gnome.org, but I can't see this "switch" everyone's talking about. I've tried both Chromium and Firefox browsers on the site. I found a similar subject on How to install GNOME Shell extensions I followed the directions but I have a warning about GNOME common dependencies. I installed GNOME-extensions-common without an error but I still cannot install user-themes, and I can't find the mysterious "switch". Any ideas? EDIT: My GNOME version is 3.4.1. (HowTos)