RSS feed integration in Firefox will let you subscribe to a feed from within the browser. I hope they use a standard feed: protocol.
A lightning bolt icon appears on sites which have the <link rel="alternate" type="application/rss xml" title="RSS" href="http://www.example.com/index.xml" /> bit in the <head> tags. All you got to do is to click on the icon and choose from the syndication formats available.