Green’s Dictionary of Slang

1. (US) a short, squat person.

2001		J. Stahl Plainclothes Naked (2002) 36: They see me walking the halls with some puto fireplug [...] normal is the last thing anyone is going to think.
2005		J. Stahl I, Fatty 29: That little fireplug in a purple turban.

2. (US drugs) a large piece of opium.

1937		B. Dai Opium Addiction in Chicago.
1938		D. Maurer ‘Lang. of the Und. Narcotic Addict’ Pt 2 in Lang. Und. (1981) 102/1: fire-plug. A large pill or ration of smoking opium, as distinguished from the common yen-pok. The pill is usually about the size of a very large pea; some addicts roll it in a cone-shape so that it fits snugly into the eye of the pipe. It is cooked on the yen-hok.
1949		Monteleone Criminal Sl. (rev. edn).