I would say that you have the res set to 72dpi, which is the default.
Print quality images realy need a resolution of 300dpi for quality output.
With nothing selected on your canvas, go to the image size dialog and change the DPI to 300.
If Fireworks asks you about resampling, click yes to resample so all the components of your image are adjusted to the correct dpi.
Note that this will make your image bloody huge in most cases, and rendering, saving and exporting may take alot longer, or even crash an older PC.
Cheers
Aaron