Master balls were introduced in the first generation of Pokemon games, and only one master ball is guaranteed during the course of a play through of FireRed on a Game Boy Advance. A master ball allows the player to catch any wild Pokemon instantly. If you wish to bypass what can be the tedious process of catching Pokemon, there are cheats that allow the player to get 99 master balls.
Pro-Action Replay is a device for the GBA that allows the user to modify Pokemon FireRed as well as other GBA games. There is no Pro-Action Replay code for 99 master balls; however, there is a code to make all pokeballs function as master balls. If you want 99 master balls, simply enter 87ACF659 707466DC 8BB602F7 8CEB681A.
Codebreakers is another device that modifies the gameplay of Pokemon FireRed. Codebreakers allows the individual to manipulate items without causing glitches. To obtain 99 master balls, enter 82003884 0001. Unlike the master balls produced by Pro-Action Replay, these balls can be traded to other players for rare Pokemon and items.
False Methods and Rumors
There is no way to get 99 master balls in Pokemon FireRed without using a game hacking device. The MissingNo glitch has been fixed in FireRed, and therefore you cannot duplicate rare items using the game's mechanics. Be wary if you attempt to use any non-hacking device related methods to get 99 master balls because they almost assuredly will fail.