From the Newtown Pentacle:
When the commanding officers of the FDNY are met with the challenges presented by a vehicle fire, their ultra modern methodologies and techniques call for the application of firefighting foam in lieu of water- which would merely spread the conflagration.
The foam extinguishes the various petroleum fed sources of the flame, and coats non burning components in a cooling embrace which suppresses further ignition. The foam spreads its expanding mass out and over any flammable material which might have escaped the vehicle and might be pooling nearby. When the foam dries out, the pictured crunchy residue remains.