Installing gnome shell extensions from extensions.gnome.org fails silently

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http://askubuntu.com – On a fresh ubuntu install (12.04, x86_64). After gnome-shell installation, I've tried to install some extensions from extensions.gnome.org but got no result. I've tried with Firefox and Chromium and got the same issue. 1- open any extension page on extensions.gnome.org 2- switch extension to "ON". Agree with confirmation about installation. 3- Nothing happens and nothing has been installed (.local/share/gnome-shell/extensions is empty). I've checked .xsession-errors, firefox's javascript console, gnome-shell console errors (alt-F2 + lg). There isn't any trace of any error. Please help :- (HowTos)