“Furnace puff-back” is talking about the explosion of soot shooting out into the home. This is due to malfunction in the fire chamber. A furnace is made to join fuel and oxygen in a balanced mix that causes control combustion. When the rate of that is slowed but the fuel is still being injected sudden and violent combustion will occur. The soot is then pushed out by the forced air.
The soot is very oily and has a sticky film to it. You might not just find this substance in the obvious exposed areas, but in closets and drawers as well. A professional restoration company will know the heating system will need to be serviced, along with the duct system. A product the company might use is a alkaline degreaser. Homeowners tend to find themselves distraught over the puff back, that is why it is so important to hire a professional. They will be able to walk you through each step and make the necessary adjustments to make sure your home is left in the pre loss condition.