We report on the third-harmonic generation (THG) of tightly focused femtosecond laser pulses at the interfaces of a cuvette filled with organic solvents. Such a system presents four interfaces separating two materials of different refractive indices and third-order nonlinear susceptibilities where the THG takes place because the symmetry around the focus is broken. We selected two cuvettes (silica and B270 crown glass) filled with different organic solvents (acetone, chloroform, and dimethyl sulfoxide) in order to have a variety of interfaces with different linear and nonlinear optical properties. For some of the peaks, the self-focusing modifies the expected cubic power law dependence for THG and as a consequence the four peak profiles may be quite uneven. Although the THG is due to the electronic part of the nonlinear susceptibility, it can suffer from the influence of the self-focusing effect, a Kerr nonlinearity that can have both instantaneous electronic and slow nuclear contributions. This mixture of two distinct third-order nonlinear processes was never considered for such interfaces. All the THG signals could be understood by taking into account the self-focusing effect. Furthermore, the nonlinear refractive indices, n(2), and third-order nonlinear susceptibilities of the solvents, χ((3)), could be determined simultaneously by the THG signals using the cuvette walls as a reference.