There are two GOOO FIR's. One that making up the landmasses of Gambia, Senegal, Cote D'Ivoire, Mauritania, Guinea-Bissau and part of Mali. You'll need an overfly permit for each within this FIR based on the route structure.
A Senegal overfly permit is only needed for flight within the Oceanic GOOO FIR.
Mali - Overfly required for landmass
Gambia - Overfly required for all flights over landmass and up to and including 20nm from the coast. Permits aren't required for flight on airways UG853 and UA602.
G-B - Overfly required for flights over landmass and water on airway UG853
Mauritania - Overfly required for flights over landmass and water up to and including 50nm off the coast.
Cote D'Ivoire - Overfly required for flights over landmass and water up to and including 50nm off the coast.