You cannot. Fireworks was never updated to be retina compatible, and since its development & support was stopped by Adobe in May 2013, it will never see an update to remedy the retina issue.
The best you can do: lower the resolution of your beautiful retina screen by half in the preferences. But that defeats the purpose of having a nice retina screen, does it not?
Unfortunately, compatibility issues like this one are only going to get worse from this point on. Perhaps it is time to look elsewhere.