Saffron city.
leaf
You first need to beat Giovanni at Silph co which is in saffron city once you do that you can go into the gym and receive your sixth badge from Sabrina.
It is not possible to get a ninth badge in Pokemon FireRed. You can only get eight badges in Pokemon FireRed.
You recieve the sixth badge after defeating Sabrina in the Saffron City gym.
Saffron city.
Fight the seventh gym on Cinnabar Island. Then fight the eighth gym at Virirdian City.
The Rainbow Badge
viridian city
spoon!
island? the fourth badge is in celadon
The 7th badge.
The 4th pokemon badge is given by Erika the Celadon City Gym Leader.