I think, in Debian 8 Jessie it worked like this:
gvfs always depends on gvfs-daemons.
gvfs-daemons recommends policykit-1-gnome, which was also a virtual
package, provided by lxsession and mate-polkit.
https://packages.debian.org/jessie/gvfs-daemons
This dependency is lost in Debian 9 Stretch:
https://packages.debian.org/stretch/gvfs-daemons
But I don't think, that this recommendation should be restored. lxpolkit
would be a much better solution for Xfce, if it could be launched
automatically.
Regards,
Hartmut Buhrmester
