The name says it all - fires a directed wall of thermite in the enemies direction.
— Description

The Firewall is a Titan Ordnance Ability that appears in Titanfall 2.[1] It is used by the class Scorch. A similar ability can be deployed in Titanfall: Assault by Core Scorch, by slamming a Maul into the ground.

Firewall fires a directed wall of thermite towards the enemies' direction. After a brief activation time, Scorch will slam his arm to the ground, causing a direct line of thermite to shoot out. The line will go towards the direction Scorch was looking at time of activation. If the line hits anything solid, including Tone's Particle Wall, it will stop. This ability can be used to trigger Incendiary Traps.

If anything human-sized is in the line, they will sustain major damage. If the human-sized enemy stays in the wall for 1-ish seconds, they will die. The Scorch kit Fuel For The Fire will allow the firewall to be activated 2 seconds early. The initial activation (The wall traveling forward) does not do any extra damage.

Firewall was buffed in Operation Frontier Shield, and is now much wider than it was previously.[2]