eohjay1,951,447 Locked 13 Nov 2014
CAUTION: THIS ACHIEVEMENT IS GLITCHY!
As with most achievements in this game, Firestarter can fail to unlock. This generally happens when an achievement has multiple conditions that need to be fulfilled and these conditions are fulfilled at different times. For instance, in my first playthrough I unlocked the Incendiary Rockets as soon as they become available (around Mission 15), and then the Incendiary Shells when they became available (around Mission 20). Doing it this way did not net me the achievement.
As with the other achievements, both of the conditions need to be fulfilled at the same time. So, DO NOT unlock the Incendiary Rockets as soon as they become available. Wait until you can unlock both the Rockets and Shells at the same time and then select them both.
Incendiary Rockets require 200 metal
Incendiary Shells require 300 metal
They should both be available around Mission 20, be sure to save up 500 Metal for this! Research them both at the same time. This unlocked as soon as they were both selected - the research did not need to be finished.