[en] Starting with the kinetic equation for an electron distribution function, we have solved the problem of mobility of two-dimensional electron gas localized over the surface of liquid helium at low temperatures. The obtained result contains the time of electron-electron scattering as well as the time of electron-ripplon interactions. The theory is valid for any relation between the times of electron-electron and electron-ripplon interactions and gives the known expressions for limiting cases. We carry out a comparison of the obtained results with experimental data and propose new experiments which allow one to obtain information on electron-electron interaction