It can use multiple Foxfire attacks period, regardless of the number of tails. While the flavor text is impressive, Foxfire is really just an unarmed attack with energy damage.
The number of tails that a kitsune has never makes a mechanical difference in PF2. This feat is an example of something that requires at least one tail to work. But unlike in PF1, in PF2 extra body parts do not translate to extra attacks.