can't add extensions via extensions.gnome.org

when i try to add an extension via extensions.gnome.org, the modal install popup appears, but clicking install doesn't install anything. an empty directory is created in ~/.local/share/gnome-shell/extensions but no files appear in it, and reloading an extension page always shows it as "off".

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: gnome-shell 3.14.0-1ubuntu1~utopic1 [origin: LP-PPA-gnome3-team-gnome3-staging]
ProcVersionSignature: Ubuntu 3.16.0-18.25-generic 3.16.3
Uname: Linux 3.16.0-18-generic x86_64
NonfreeKernelModules: nvidia wl
ApportVersion: 2.14.7-0ubuntu2
Architecture: amd64
CurrentDesktop: GNOME
Date: Tue Oct 7 13:24:27 2014
DisplayManager: gdm
GsettingsChanges:
 b'org.gnome.desktop.interface' b'clock-show-seconds' b'true'
 b'org.gnome.desktop.interface' b'gtk-im-module' b"'gtk-im-context-simple'"
 b'org.gnome.desktop.interface' b'clock-format' b"'12h'"
 b'org.gnome.desktop.interface' b'text-scaling-factor' b'1.5000000000000004'
 b'org.gnome.desktop.interface' b'clock-show-date' b'true'
InstallationDate: Installed on 2014-02-24 (225 days ago)
InstallationMedia: Ubuntu-GNOME 14.04 "Trusty Tahr" - Alpha amd64 (20140218)
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-shell
UpgradeStatus: Upgraded to utopic on 2014-08-17 (51 days ago)