Ralf Herrmann recently took a look
at the new typography features found in Firefox 3, pitting them against what's been available in Safari 3 for a while. The results show some major advances, and some major problems. The current OpenType or Apple Advanced Typography features in Firefox 3 include promising features like basic ligatures, which is exciting to those who live and breathe typography, but it fails in some non-English languages. Overall, it seems there are a lot of would-be nice new features that don't quite provide enough detail to be universally helpful. But it's a step in the right direction.
Check out the post at Ralf Herrmann's Typography Weblog for a very complete overview and comparison.