Well, firefox is really good as a straight up browser, I haven't found one that I like better.
Flock, built on the same engine as Firefox, is, however, really really good as an extended functionality webtool. Being an extended set of tools, it is pretty bogged down by it as well. you can't have TOO many RSS feeds, you can't be signed into too many networks at a time etc - these things cause the application to slow, especially when you are checking them, which is the whole reason to use it - for faster access. It's still a very powerful tool, especially for marketing (one that I should probably reinstall too

)
I like Chrome, but meh, it's TOO minimal. It's really good as a web browser - what I mean in this case is that it renders fast as hell and it has a really really good javascript module, but it doesn't help me in moments where I need to tap into something not just back, stop, go, refresh related, yea? Incognito mode is cool, but only for it's skin. The incognito name is misleading as you are still wide open to the outside world, just that your family cant snoop you.
The thing is, though, it lacks a lot of functionality that I may not need for every site, but always end up needing once or twice a day.
Since firefox extensions work in Flock (Y.M.M.V.), flock is the easy winner here because of it's functionality amongt social and web 2.0 platforms - this does not beat Firefox as a broweser, but it beats firefox in usability and making my things "accessible".
That being said, I mainly just use Fx browser now, and that's why it got my vote.