For the problem of full compressible Euler Equations with variable entropy coupled with a nonlinear Poisson equation in three spatial dimensions with a general free boundary not restricting to a graph, we identify a stability condition for the electric potential of which the outer normal derivative is positive on the free surface besides the Taylor sign condition for the pressure to obtain a priori estimates on the Sobolev norms of the fluid variables and bounds for geometric quantities of free surface. This talk is based on a joint work with K. Trivisa and H. Zeng.