A self-adapting gas turbine firebox with variable geometry includes at least one system with variable opening for automatically adjusting a combustion configuration inside a combustion chamber according to an air temperature, particularly of air from a compressor. The adjustment is performed by a thermosensitive member that controls at least one cross-sectional area of a passage to the combustion chamber, for air which participates in the combustion of fuel or participates in a dilution of gases effective inside the combustion chamber.