Question

What are all the differences between Fire Red and Leaf Green?

Answer 1

Besides version exclusives, the in-game trades are different. Firered reuses Pokedex entries from the original Red and Green and Silver, and Leafgreen reuses Pokedex entries from the original Blue, the localized Red and Blue, and Gold. When the player deletes a save file in the Japanese versions, the screen is teal in Firered and blue in Leafgreen.
source

Comments

Also, aren't the Safari Zone encounter rates different, with Nidorino for FR and Nidorina for LG in certain areas?

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There are lots of encounter rate differences. If you want all of them, I can convert this answer to a comment.

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If you think that the encounter rates should be on there for completeness, go ahead, but if you think they are unnecessary, then feel free to leave your answer as it is. You're more experienced than me.