I think the problem was I installed the url master module first, then uninstalled the module and use the iFinity.FriendlyUrlProvider.dll instead. Not sure why the uninstallment was not complete - I can still see the Friendly Url Settings under host menu, but just showing an empty page when click it. I've also manully removed the URL Master folder under DesktopModule. But the FriendlyUrlProvider can not work properly.
However I installed a fresh DNN4.8.4 and FriendlyUrlProvider, they work toghter fine.