Self-adapting gas turbine firebox with variable geometry, comprising: - a combustion chamber; - an air supply system, in particular for supplying air exiting a compressor, arranged to supply the combustion chamber with at least one stream of air having a variable temperature; and - at least one system with variable opening, comprising:. an intake passage, arranged to allow the stream of air coming from the air supply system to enter the combustion chamber,. a movable closure member, which changes an open cross-sectional area of the intake passage when moved, and. a thermosensitive member, having a shape which varies depending on a temperature of said thermosensitive member, the thermosensitive member being arranged in the stream of air between the air supply system and the intake passage, and being connected to the closure member so that a deformation of the thermosensitive member causes said closure member to move, wherein the intake passage is arranged with respect to the combustion chamber so that the air entering said combustion chamber through said intake passage is air that participates in the combustion of a fuel in the combustion chamber, or air that participates in a dilution of gases effective inside the combustion chamber, so that the turbine firebox is self-adapting for automatically adjusting a combustion configuration inside the combustion chamber, according to an operation power setting of the turbine firebox, wherein the system with variable opening is arranged to vary an intake flow rate of combustion air coming from the air supply system and entering the combustion chamber through an air supply swirler located axially upstream of said combustion chamber, relative to a general direction of the flow of air into the combustion chamber during operation, characterized in that the closure member comprises a ring with openings which laterally surrounds the air supply swirler, so that the openings are aligned or offset relative to channels of said air supply swirler, in order to vary a cross-sectional area of an access to said channels according to an angular position of the ring around the air supply swirler, forming the open cross-sectional area of the intake passage. - a combustion chamber; - an air supply system, in particular for supplying air exiting a compressor, arranged to supply the combustion chamber with at least one stream of air having a variable temperature; and - at least one system with variable opening, comprising:. an intake passage, arranged to allow the stream of air coming from the air supply system to enter the combustion chamber,. a movable closure member, which changes an open cross-sectional area of the intake passage when moved, and. a thermosensitive member, having a shape which varies depending on a temperature of said thermosensitive member, the thermosensitive member being arranged in the stream of air between the air supply system and the intake passage, and being connected to the closure member so that a deformation of the thermosensitive member causes said closure member to move,. an intake passage, arranged to allow the stream of air coming from the air supply system to enter the combustion chamber,. a movable closure member, which changes an open cross-sectional area of the intake passage when moved, and. a thermosensitive member, having a shape which varies depending on a temperature of said thermosensitive member, the thermosensitive member being arranged in the stream of air between the air supply system and the intake passage, and being connected to the closure member so that a deformation of the thermosensitive member causes said closure member to move,