Bug#656578: Can't install extensions from gnome site (exception in /usr/share/gnome-shell/js/ui/extensionSystem.js)

[Olivier Cailloux]

https://extensions.gnome.org/extension/55/media-player-indicator/ also 
fails. Some extensions work, e.g. 
https://extensions.gnome.org/extension/6/applications-menu/ (just 
installs without prompting for anything).

remove accessibility also fails with a fresh user, just added through 
gnome control panel. Same error in .xsession-errors.

I don’t use a proxy, and the proxy system settings are correct (no proxy).

I don’t know how to use and what to check for precisely using tcpdump.

curl does not give any error message. It only says:
$ curl https://extensions.gnome.org/ > /dev/null
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 7528 0 7528 0 0 6960 0 --:--:-- 0:00:01 --:--:-- 7294

I assume it means the certificate causes no problem and therefore I 
didn’t check the rest, regarding the certificates.