"Best of the best"4.5 starson by Raithlin
Pros: Extensions, open source
Cons: Still young
Summary: Interesting to note that the comparison gives Firefox 2 a no for tab history, crash recovery, etc. While this may be true for the base product, this is all available now in Firefox 1.5 via extensions (Tab Mix Pro).
What I also found stunning is that, as per 1.0 - 1.5, FF2 has taken the best extensions and made them part of the next base release. This is the way of the future, and the reason (IMO) why Opera and IE, as good as they may become, will not be able to keep up with Firefox in the long run.