A self-consistent extended fluid-dynamic model describing a focused microwave discharge in a molecular gas is developed, and numerical simulations of the formation of plasmoids in nitrogen in an experimentally operating cylindrical paraboloid focusing system are carried out. It is shown that, depending on the input power and gas pressure, plasmoids ranging from one to four can be formed. The main spatial-temporal parameters of the plasmoid formed at the main focus of the system are studied in the active phase and in the afterglow phase. The main channels of gas heating in the domain of plasmoid formation are investigated. The importance of taking into account gas heating in the self-quenching reactions of excited nitrogen molecules, both in the active phase and in the first microseconds of the afterglow phase, is shown. The main mechanism at long times in the afterglow phase is the release of energy in vibrational-translational relaxation.