In Pokémon FireRed and LeafGreen, players need money for healing Pokémon, buying items, and much more. There is a bug that helps you earn money quickly. This is known as the Nugget Bridge glitch. It works in the English version of the game.
To use this glitch, first defeat Gym Leader Brock in Pewter City. Then, move through Mt. Moon and Route 4 to Cerulean City. At Nugget Bridge, you must defeat your rival and five other trainers. After beating the fifth trainer, save your game and go back to the Pokémon Center.
Deposit all your Pokémon except one low-level Pokémon, like a Level 3 Weedle. Go back to Nugget Bridge, and the man there will give you a Nugget. Let him defeat your low-level Pokémon. You will return to the Pokémon Center, but keep the Nugget.
Keep battling the man. Each time you lose, you can get another Nugget. Each Nugget sells for 5,000 Pokedollars. You can make a lot of money this way! Make sure to battle and collect as many Nuggets as you want.