No... FireFly batteries can not be "desulfated" in the normal sense of the word.
If they are operated at a partial state of charge for multiple cycles, they apparently can show some temporary capacity decrease. The manufacturer's recommended procedure for recovering that capacity is to discharge them all they way down to dead empty (10.5 volts) and then do a normal charge back to full.
I do not know what chemistry is happening inside with that procedure.
Cape Eleuthera, Bahamas
Heading north tomorrow... probably!