I'll leave the image of you shaking your can, to the ladies.
Class B fires, flammable liquids and gases, solvents, oils, greases (excluding cooking oils/greases in depth) tars, oil-based paints and lacquers, (yeah, I had to check) keep flaring up because the fumes are reignited by what's still burning? Do they stop flaring once the flames are completely extinguished?
I guess the AFFF would suppress the flammable vapors from reforming while you get the flames beaten down.