Integration with Firefox

Automatic method

Go to Preferences -> Feeds and scroll down until you see the button named "Click here to register this site as a feed reader". Click on it to register your tt-rss installation with Firefox.

Manual method (obsolete)

To subscribe to feeds in Firefox 2.0 with tt-rss add the following lines to your user.js (you'll need to replace URL in the third line with full URL to your tt-rss' instance backend.php:

user_pref("browser.contentHandlers.types.nr.title", "Tiny Tiny RSS");
user_pref("browser.contentHandlers.types.nr.type", "application/vnd.mozilla.maybe.feed");
user_pref("browser.contentHandlers.types.nr.uri", "http://your.domain.dom/url-to-tt-rss/public.php?op=subscribe&feed_url=%s");

Where nr is first available number for new feed reader, if you didn't add anything else it should be 4. Some more details are available in this tutorial.