Boston firefighters are jakes, but why?

Jake is a derogatory terms for police in Boston and some places in the northeast. At least in 'urban culture' I'm not sure why. I never knew Jake was for firefighters.

Speaking of origins, Luc Sante wrote (in reference to NYC, but probably true of other places) that the first fire companies were street gangs with fire equipment. Sante was an advisor for the film "Gangs of New York."

I assumed that all US fire fighters were called jakes. The WGBH piece doesn't really address that, admittedly less than pressing, issue.