Crackers, what what?

Laura is concerned that "LondonCrackers" may require some explanation, so here goes:

crack•ers [krak-ers] pl. noun

1. persons born and raised in the southeastern United States, esp. Florida natives
2. a small paper roll used as a party favor, containing candy or trinkets, which explodes when pulled sharply at both ends
3. colloquialism for the mentally irregular (inf. slang; see also “balmy,” “barmy”, etc)

“What cracker is this same, that deafs our ears

  with this abundance of superfluous breath?”

—W. Shakespeare, King John, Act II Sc. 1, 1595

As to which meaning was meant, well, that is left as an exercise for the reader :-)

(A fourth definition suggested itself, but there's no need to be perjorative now, is there?)