One can launch automatically the demexp GTK+ 2.x client on a demexp URL by adding following line to file .firefox/default/xxxxx.xxx/prefs.js in your HOME directory (xxxxx.xxx is generated randomly at Firefox installation and is specific to your account). Be aware that Firefox should not be started when doing this modification:
user_pref("network.protocol-handler.app.demexp", "/usr/bin/demexp-client-gtk2");
Once this modification is made, following URL should launch the client demexp://tuxinette.linux-france.org:50000.
Following URL are doing specific actions with the GTK+ 2.x demexp client:
demexp://server[:port]
demexp://server[:port]/browse/question/NN
demexp://server[:port]/vote/question/NN