best firestorm support gems

Non crit based, which would be the best? The burning gems?the aoe gems? Faster casting?

depends..

burning/ignite certainly not - FS does lot of small hits which is no good for burn

fire penetration - highly recommended - lots of enemies have lots of fire resistance

aoe+conc effect,faster casting, inc duration are popular choices

Crit and burning aren't that useful because firestorm consists of many small "hits". Go for longer duration, fire pen, concentrated effect, increased aoe and maybe faster casting

Cool, thx guys.

Conc effect, fire pen, faster casting, iron will, added chaos, increased duration, increased aoe are all quite viable. If you are buffing FS with a lot of spell damage (as opposed to fire/ele damage), added chaos becomes quite attractive because it does not reflect.

I prefer no increased aoe combined with conc effect + increased duration (nodes, not gem) because it makes FS dps much more predictable and a viable single target threat. My 5L would be conc, FC, pen, iron will. Aiming for around 200% overall increased damage and 45% increased duration from tree. Swap out pen or will for LL if reflect maps are a problem. Spell block is the best defense vs thorns and reflect (both will be a problem) and you should aim for 75%. The other major obsticle is the mana cost, GL. Shoot me a pm if your interested and I will send you my tree and the theory behind it.