If past sales are any indication, a rare Boba Fett action figure, produced by toy maker Kenner , could command a blockbuster sum at auction. The figurine is a prototype created by Kenner as part of its Star Wars mail-away series in 1979. Unlike the other static toys on offer, though, the Boba Fett figure came with kinetic rocket-firing capabilities. A hundred prototypes rolled off the line, 70 with L-shaped firing slots and 30 with J-slots. But upon testing, the toys were deemed unsafe for children and never mass-produced. The Boba Fett toys that were eventually released had welded-on missile packs. The specimen now up for sale at Goldin on June 3 is one of a scant two-dozen examples known to exist since the Boba Fett prototypes were discovered by hobbyists in the 1990s. Unlike most J-slot models, this one is painted, its surfaces bearing few of the marks of quality testing.…