In order to activate its effect, “Fox Fire” must be face-up when the attack that destroyed it was declared (like “Atomic Firefly”). If a face-down “Fox Fire” is attacked, its effect is not applied even though it is face-up when destroyed.
While “Skill Drain” is active, you can Tribute “Fox Fire” for a Tribute Summon.
If the opponent controls your face-up “Fox Fire”, and it is destroyed as a result of battle, it will be Special Summoned to your (the owner’s) side of the field during the End Phase.