Substitua o Thunar pelo Nautilus na configuração de sessão do Xubuntu:
sudo nano /etc/xdg/xdg-xubuntu/xfce4/xfconf/xfce-perchannel-xml/xfce4-session.xml
De:
<property name="Client3_Command" type="array">
<value type="string" value="Thunar"/>
<value type="string" value="--daemon"/>
</property>
Para:
<property name="Client3_Command" type="array">
<value type="string" value="nautilus"/>
<value type="string" value="--no-default-window"/>
</property>