It is not possible to get a ninth badge in Pokemon FireRed. You can only get eight badges in Pokemon FireRed.
There is no ninth badge.
The fifth badge in Pokemon FireRed is the Soul Badge. You can earn the Soul Badge by defeating the Gym Leader Koga in Fuchsia City.
The Rainbow Badge
to the forest
In the saffron city gym beat Sabrina to get the badge.
The 4th pokemon badge is given by Erika the Celadon City Gym Leader.
The boulder badge, the cascade badge, the thunder badge, the rainbow badge, the soul badge, the marsh badge, the volcano badge and the earth badge.
beat the gym leader