It is clear that some countries worked with these prefixes in 1927-1928, and then switched to others, more familiar to us, some continued to work with these prefixes in the following years.
FA Abyssinia (currently - Ethiopia and Eritrea)
FB Madagascar
FB Reunion
FB Comoros
FB Juan de Nova
FB Glorioso
FB Tromelin
FC Belgian Congo
FC Ruanda
FC Urundi
FD Angola & Kabinda
FE Egypt
FF French Sudan
FF Mauritania
FF Senegal
FF French Guinea
FF Ivory Coast
FF Upper Volta
FF Dahomey
FF Civil Territory of Niger
FF French Togoland
FG Gambia
FH Italian Somaliland
FI Italian Lybia (Tripolitania & Cyrenaica)
FJ Somaliland Protectorate
FJ Socotra
FK Kenya
FK Zanzibar Protectorate
FK Uganda
FK Anglo-Egyptian Sudan
FK Tanganyika Territory
FL Liberia
FM Tunisia
FM Algeria
FM Morocco (including the Spanish zone)
FM Tangier
FN Nigeria
FO Union of South Africa
FO Northern Rhodesia
FO Southern Rhodesia
FO Bechuanaland Protectorate
FO Southwest Africa
FP Portuguese Guinea
FP Cape Verde
FQ French Equatorial Africa
FQ Cameroons
FR Rio de Oro and adjacent Spanish Zones
FR Ifni
FR Canary Islands
FS Sierra Leone
FT Eritrea
FU Rio Muni (Spanish Guinea)
FU Fernando Po
FV French Somaliland
FW Gold Coast Colony
FW Ashhanti
FW Northern Territories
FW British Togoland
FX Seychelle Dependencies
FZ - Mozambique
List Courtesy of R0L-123