I'm currently using Nightly UX. I've been using it for quite awhile and I haven't had any problems with it. That being said, you should keep in mind that this is a pre-alpha release and it wouldn't be surprising to run into some problems. If your browsing experience heavily depends on extensions, I'd recommend you not to use Nightly, though. I only use NoScript and AdBlock Edge as my extensions, but if you install 10+ extensions, you're not gonna like Nightly.
In any case, you can just install it and experience it yourself. If you're like me who started using Chrome because you were sick of how slow and unstable Firefox was, you'll be amazed how good it is now.
I've used Firefox all my life because of Firebug. Then after a while it just got so slow that it was unusable and the experience became terrible. And then I switched to Chrome. I'm not fond of their developer tools as much. Not as good as Firebug. I guess I'll give FF another shot.
I switched for the same reasons but kept FF around mainly for Firebug. After using and getting use to Chrome Dev Tools, it is actually no different and in some cases better. I don't do as much front-end dev as I used to though... But I do remember reading that the FF team worked with developers of popular plugins like Firebug to help make those plugins run better, use less memory and cause less memory leaks. You may find those plugins a lot better now.
In any case, you can just install it and experience it yourself. If you're like me who started using Chrome because you were sick of how slow and unstable Firefox was, you'll be amazed how good it is now.