Flamethrower

Napalm

 * Napalm sticks to and burn targets, increasing initial damage and dealing damage over time per stack (maximum 12 stacks, or 24 stacks for 2 Flamethrowers or more).
 * Lasts 3 seconds.

Fuel Discharge

 * Discharges pure, pre-ignited fuel at the target, dealing damage and reducing armor in a cone and applying Napalm stacks.
 * Deals an additional 30% damage to armored units.
 * Do not friendly fire.
 * Damages air units.
 * Each level improves energy, fuel cost, number of stacks applied and damage.

Plasma Shield

 * Activates a damage-abosorbing plasma shield specially built into your suit for a short duration.

Graviton Grenades

 * Throws a graviton charge at a target point, pulling all nearby units towards the center.
 * Each level imroves pull strength, radius, and duration.

Recommended Skill identifers
Flamers only start with 205 energy; putting that into consideration, I highly recommend the EN (Energetic) Skill Identifier (SI). On higher difficulties you will find that the flamer is very energy starved.

For your second SI, I recommend something that can get you in and out of fights easily, so you don't risk having to unnecessarily activate your shield when you are running instead of tanking. Therefore, TT(TwinkieToes) works well to up your movement speed. If you are going to focus on max level fuel discharge, WK(WhizKid) synergizes well to take down hordes of charging hunters (one-hit in normal difficulty with WK, two hits in higher difficulties)

Recommended Builds
(Napalm 1) > Fuel Discharge 4 > Plasma Shield 1 > Napalm 1 > Soldier Skills 1 > Plasma Shield 4 > Napalm 4