Minn and the others are correct, fiberglassing the firewall is not needed. IF you feel like you need more strength than triangle stock will give you, then you should pin the firewall. after epoxying the firewall to the fuselage drill through the fuselage and into the firewall. use carpenter's glue in the hole and then tap in a wooden dowel. cut the dowel flush with the fuselage. This is cleaner than fiberglass. it is lighter than fiberglass. and is easier than fiberglass. Built this way, you won't be able to pull the firewall out.