I suppose a manager is also an employee, but Manager inherits from Employee with a .fire() method seems wrong, no? I'd expect a method which takes another object or ID, not to change the state of the object with the fire() method.

Anyway, this is why I stay far, far away from OOP when I can - vast amounts of time spent on these questions which generate zero insight (at least the mathematical obsession with some parts of FP can be fun)