Buildings FF on
Tyrant charge FF off, but x4 kickback.
Goon punce FF off, but x2 kickback.
Booster poison FF off.
Adv Mara zap FF off.
etc.. alien claws FF off, but 1 point damage.
Normal humans weapons FF off, but 1 point damage.
Damage for grenades FF on.
Flame/lucy self-damage FF on.
I like the kickback alternatives to FF for aliens. Charge and pounce really shouldn't do team damage, they're methods of transportation 2/3 of the time.
Mara zap doesn't do team damage to my knowledge, since it only chains between enemy units.
Grenades should have FF, but the thrower needs to have an automatic sound byte saying "Grenade!" the instant he throws it.
Luci/Flame FF needs to be off, since there's no way you can use them in a group without completely destroying your own team. Some people may consider it fair to have FF on for them, but doing so will make all Flamer/Luci users go rambo, which isn't good.
Although I could live with FF on for the rest of the weapons/slashes, it's much better with it off. Building FF, however, should be on, otherwise flamers/lucis can protect a base by spamming fire over everything.