Fonts in Windows programs are now really system fonts. i.e. They aren't Fireworks fonts they are Windows fonts and stored in a folder called Fonts. Any font file you copy there is available to any program that wants to use them... like Fireworks.
Search fonts or free fonts for plenty of sites... many of which are click traps. Here's one I use: [acidfonts.com...]
Download any font, unzip and copy it to your C:\WINDOWS\Fonts\ folder. (Sometimes you have to restart Fireworks for the new fonts to show in the Fonts menu.)