Feed Preview by Guido Berhörster

Feed Preview is a Firefox Addon which indicates the availability of RSS or Atom feeds in the browser's URL bar and renders a previews of feeds.

Feed Preview has the following combination of features which are unique in combination and set it apart from similar feed previewing addons:

• Extensive feed format support: robust parser which handles the RSS 1 (0.9, 1.0), RSS 2 (0.91, 0.92, 0.93, 0.94, 2.0), and Atom (0.3, 2.0) feed families including obscure features, supports non-UTF-8 character sets, and uses content sniffing to detect feeds served with XML or RDF content types
• Media files: support for enclosed media files which can be downloaded from the preview page
• Subscription support: allows subscribing to feeds using user-configurable web-based feed readers and ships with presets for frequently used services and integrates with addon feed readers
• Secure: HTML content/summaries are displayed in sandboxed iframes, all other elements are sanitized
• Preserves the feed URL: the preview is generated via stream filters before it hits the rendering engine, there are no redirects and the "View Source" function works as expected
• Modern design: Follows the Photon design guidelines and integrates seamlessly with Firefox
• Open source: published under the MPL 2.0
• Internationalization: the code is fully internationalized, user submitted translations are welcome