I have found an open-source alternative that seems to offer some services similar NewsfireRSS.
Vienna is a freeware, open source RSS/Atom newsreader for the Mac OS X operating system. It provides features comparable to commercial newsreaders, but both it and the source code are freely available for download.
http://www.opencommunity.co.uk/vienna2.php
http://www.opencommunity.co.uk/blog.php