Pros: Good security suite.

Cons: A major headache for any app using Flash Player.....which is nearly every website with video. Despite knowing of this problem, Mozilla is doing nothing to resolve the issue.
Summary: Do not DL until application issues are resolved.

This is currently my browser of choice on Mac (although I'll be looking closely at Chrome when it comes out too). The biggest benefit of it are the plugins which let you add time saving features like mouse gestures. Safari is faster to load on Mac and has some other small UI improvements I like better than Firefox, but Firefox wins (just barely) overall in my book.