Interesting ... the /usr/share/applications/defaults.list simply isn't present (where did it go?), and neither is ~/.local/share/applications/defaults.list.
And according to the latest documentation I have, it seems that xdg-open is broken. (I'm using Arch, so see here:
https://wiki.archlinux.org/index.php...it_should_work )
I'm sure there's a workaround somewhere. I'm working on it.