That's the way Fireworks has always worked. I'd like to see that changed as well. :-) Here's the URL of the Adobe Feature Request/Bug Report form.
Apologies for resurrecting this question thread, but I'd like to correct that this has not been the way Fireworks used to work.
I've successfully used font management software (Suitcase, MainType) for Windows, and up to FW CS3 on Vista x64 you could activate a font and it would appear on FW's font list without restarting the application. If you had text object selected when activating a font you only had to deselect the text object and select it again to get new fonts to the list.
We've just now made an "upgrade pitstop" to CS4 versions, and now there seems to be no other way to refresh font menu in Fireworks than restarting the app as Linda mentioned. Hopefully CS5 will have some improvement on this, otherwise I'll fill that mentioned wish form
My understanding is that CS5 does address this issue.
Indeed it did! Thanks to all CS5 engineers!
Fireworks is now able to refresh the font list without restarting, reloading the document or even deselecting the text object - nice
(also Flash is now much smarter with font activations than previous versions)