The key is either useless (genuine) or dangerous (cracked). Let Fireworks 8 rest in peace.
Adobe shut down the activation servers for legacy Macromedia products, including Studio 8 (which contained Fireworks 8), on December 15, 2012. Macromedia Fireworks 8 Key
The time spent hunting for a working key, bypassing activation, and fighting compatibility issues is better spent learning modern free alternatives that are safer and more capable: The key is either useless (genuine) or dangerous (cracked)