No it's not possible. No method of trading where designed to trade between these games.
You have to trade it from Fire Red
You can't. have to trade from fire red
You have to trade with someone who has fire red.
you can not catch teddiursa in either leafgreen or firered. you have to trade it.
You cannot get to Fire Island on Pokemon LeafGreen. Fire Island is a setting exclusive to the second Pokemon movie, Pokemon the Movie 2000.
yes you can trade pokemon leafgreen pokemon to pokemon emerald version same as pokemon fire.
YES
You have to trade it from Fire Red
You can't. have to trade from fire red
you have to trade from fire red
yes.
Sorry, but you have to trade it from fire red.
You have to trade with someone who has fire red.
Trade it from leafgreen or fire red
cant you have to either trade from pokemon leafgreen or fire red
you can't
No, you cannot trade between the two different versions because the Pokemon are different or the Pokemon know different moves that are not in red version. When they re-make gold and silver for DS there may be some way to trade between Pokemon fire red and leafgreen to the new gold and silver but I doubt it.