Firefly is NERF in patch, cost almost 2x more fuel, and more manpower, and has much less Rate of Fire. It is not suitable counter for Stug.
Firefly
Due to the Firefly's range and accuracy, when combined with the Comet or when multiple Firefly's are fielded, this combination of tank power can prove to be overly dominate (primarily in team games). To compensate, the following changes have been made:
Accuracy from 0.08/0.07/0.05 to 0.06/0.05/0.4
Moving accuracy from 0.75 to 0.55
Tulips no longer cancels move commands upon stun when hit
Tulips now deal 33% damage versus infantry.
Vet 3 damage bonus reduced from +80 to +40
interesting how you come to the fuel thing