Thanks Genghis.
I just assumed that thin asbestos panels, such as asbestos insulation board might have been used due to its fireproof properties. I found some reference that is was used in firewalls of WWII aircraft such as the hurricane where an asbestos panel was sandwiched between two aluminium panels.
http://www.jneaircraft.com/am274/2008-2/
Also, someone mentioned that the material attached to the cockpit side of the firewall used to dampen the engine noise might contain asbestos.
I guess I'll see if it mentions it on the technical manual if I can find a copy...
Cheers