RSS has nothing to do with a browser, it's a completely different protocol. As Tom says, FeedDemon is a standalone app specifically for RSS, while the browser addins and Thunderbird feature are OK, but they don't have the power of a dedicated application. There are some free RSS readers but none with the power and flexibility of FeedDemon and I've looked at quite a few. For the casual RSS user, either Sage for FF or Thunderbird will be sufficient. I review dozens of RSS feeds daily so I need the power of a dedicated program.