Thanks for your feedback! However I'm not quite sure what you mean: Isn't the first entry in the "Desktop" section "Windows / Firefox 56" for you?

Adding new User-Agents for different Windows versions is unlikely to happen as they are IMHO not sufficiently different from the existing entries to justify making the list longer than it already is. There also is currently unresolved question on how to keep the list from becoming stale without too much reoccurring labour.