Onset of Marangoni convection in a horizontal layer of fluid possessing a deformable free surface and subjected to a nonplanar oscillation of shear due to motion of the lower plate is studied. Results show that the onset of the Pearson mode occurring at finite wavelengths is delayed by the nonplanar shear, but also that the long-wavelength mode, originally studied by Scriven and Sternling, is destabilized. The modulational effect peaks at a finite frequency and tends to zero in both small and large frequency Limits. Physical mechanisms for both stabilization and destabilization are discussed.