reinstalling all of xfce now works to the point of simple run in terminal.
However, I see a wide variation of how freedesktop items are handled.
LXDE works the way I would think it should, i.e., within a .desktop item using both
Exec=sudo usbinstall and Terminal=true, works as expected. XFCE does not. Even back to the run command prefixing with sudo fails, but of course, not checking run in terminal, and using
aterm -e sudo usbinstall does.