I've played Fire Red over 50 times and never realized that spaces with hidden items have a special mark so you can find most of them even without the item finder :
Pokemon FireRed and LeafGreen :: Full Walkthrough
Team Rocket's Hideout - Pokemon Fire Red and Leaf Green Guide - IGN
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Pokemon Fire Red - Secret Cave of Viridian City - Jirachi - YouTube
How to Get Good Pokémon in Fire Red: 4 Steps (with Pictures)
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Pokemon FireRed and LeafGreen :: Full Walkthrough
Pokémon: 10 Things You Missed In FireRed & LeafGreen
8 SECRETS & EASTER EGGS in Pokemon FireRed & LeafGreen You Missed - YouTube
How to get Mewtwo in Pokémon Fire Red? How does that differ from Leaf Green - Quora
How to capture Moltres in Pokemon Fire Red - Quora, moltres fire red - thirstymag.com
Pokémon FireRed: A Step By Step Guide To Getting Fly
What is the fastest way to get money in Pokemon Fire Red? - Quora
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Safari Zone - Pokemon Fire Red and Leaf Green Guide - IGN