How do you get Celebi in Pokemon FireRed?

Answer 1

Celebi cannot be captured officially in any English game. In order to get it in Pokemon FireRed you will have to obtain it by trade. It has been given away in promotional events as well.

In the Japanese version of Pokemon Colosseum you can obtain Celebi by purifying all 48 shadow Pokemon and then using the bonus disk. This however only works for a Japanese game.

Also, in the Japanese versions of Pokemon Crystal a GS ball could be obtained through the Pokemon Mobile System and when put on the shrine in Ilex Forest Celebi would appear.

In the English version of Pokemon Crystal a game shark or other cheating device could be used to create the GS ball and gain Celebi.

See links at left for information on obtaining Celebi.

When you preordered Colosseum in America, you got a bonus disc that came with Jirachi. The Japanese version of this bonus had Celebi on it instead of Jirachi. So your two choices are to buy a Japanese bonus disc somewhere or wait for a Nintendo Event.
It's not possible to get celebi in firered the only legit way is to receive one from the special disc of Pokemon colosseum but only the Japanese version of it that is. You will need to cheat otherwise.