EDIT: I think I managed to solve it thanks to @nikgnomic link.
I figure out that it is due to the use of the org.freedesktop.FileManager1 d-bus service from nsGIOService.cpp - mozsearch . The solution is to change the implementation of the d-bus service (see /usr/share/dbus-1/services/org.xfce.Thunar.service).
For example, for Thunar we have the following in /usr/share/dbus-1/services/org.freedesktop.FileManager1.service:
[D-BUS Service]
Name=org.freedesktop.FileManager1
Exec=/usr/bin/Thunar --gapplication-service
SystemdService=thunar.service
I changed /usr/share/dbus-1/services/org.xfce.FileManager.service to contain the following content:
[D-BUS Service]
Name=org.freedesktop.FileManager1
Exec=/usr/bin/nemo --no-default-window
SystemdService=nemo.service
I don’t think this is the cleanest of solutions but it works! So I have to ask: IS THIS SAFE TO DO?