Add the code below into your fluxbox's startup
script (i.e. ~/.fluxbox/startup), after "Start
DBUS session bus:" code section, or just above
the line "exec fluxbox" :

8<-------------------------------------------
# Start XDG compliant startup tool
#
if [ -x /usr/bin/fbautostart ] ; then
  /usr/bin/fbautostart &
fi
8<-------------------------------------------