This makes Andrew G. McCabe acting FBI director. He's in the civil service, not a Presidential appointment. He was an FBI agent and worked his way up. From what little is available about him, he seems to be good at the job.[1] As civil service, he can only be fired for cause.
Appointing a new FBI director requires Congressional approval, and will be controversial.
[1] http://www.latimes.com/nation/na-la-fbi-deputy-director-2016...