That would be a colossal mistake. Fire Rosenstein instead and replace him with someone who would rein in Mueller by forcing him get back on track and narrow the focus back onto his originally charged investigation of collusion and make Sessions feel truly threatened for his very life, job and future thus forcing him to appoint that special prosecutor to investigate the deep state which Sessions is part of and where Mueller is a ranking lieutenant and Obama is the head of the Hydra like conspiracy in the deep state cabal and its attempts at overthrowing a legitimately elected President in a coup attempt.
Firing Mueller doesn’t preclude firing Rosenstein. But Rosenstein is the one who recommended Comey be fired - he needs to appear again and explain why he can recommend Trump fire Comey, and then turn around and appoint a SC because Trump fired Comey.
As to Sessions, dream on that he will “feel truly threatened” by any of this. He’s protected, even by the same Dim senators who voted against is appointment.
POTUS DJT has nothing to lose at this point by firing Mueller, and more to lose if he doesn’t