How do you use the powder jar in Pokemon fire red?

You can't use a powder jar in Pokemon Fire Red. There's no item with that name in the game.

Are you thinking of a different item? Perhaps you're thinking of:

* Powder: This item increases the power of Normal-type moves. You can find it in various locations, like the Poké Mart in Viridian City.

* Smoke Ball: This item helps you escape from wild Pokémon. It can be found in the Game Corner in Celadon City.

* Dustox: This Pokémon is a Bug/Poison type and is found in the Hoenn region, not in Fire Red.

If you're looking for a way to use a specific item in Fire Red, please provide more details, and I'll be happy to help!