Except the Intro, they look exacly IDENTICAL to me.Where are the differences ?
there are some wild Pokemons that are for leafgreen or firered
this link is for the different Pokemons http://www.serebii.net/red_green/exclusives.shtml
There are some Pokemon that cannot be found in Firered that can be found in Leafgreen and vice versa.
This Link will show you the Pokemon.