As I'm sure you're aware, Firefox 3.5 was released recently. If you haven't already, I would suggest updating(:
A large bonus is their support for a whole slew of CSS 3 features. Their developers page for 3.5 serves as a great resource for checking the
-moz specific CSS features, as well as a nice refresher on some of the more complicated CSS 3 features in general. This plus Safari 4's ongoing CSS 3 awesomeness opens plenty of doors for doing some cool stuff. With the two main (good) browsers supporting so many CSS 3 features, plus Firefox's astronomical update rate, the time to start using this stuff is now.