Yes, Trump had people fired, including the director of the FBI. And he even admitted he did it in hopes it would stop investigations into his shady activities. That doesn't make the director (a Republican) a bad guy or corrupt. Trump is a vindictive guy and as president he can get people fired. Interestingly, for a guy whose most famous phrase (written for him by TV writers) was "Your fired!" But he never had the balls to fire anyone face to face in real life. He wouldn't even do it on the phone. He had someone else do the job.
From what I've seen they got fired for disagreeing with Donald Trump, who, while he wasn't an educated or experienced or knowledgeable or even an intelligent man, felt his 'gut' told him what was right after watching FOX.
Now you see that's where you and Donald keep making mistakes. Neither the FBI nor the Justice Department are his attorneys. Their loyalty is to the law and constitution, not Donald Trump.