There may be a release candidate, but consider this. It’s now Sunday morning where I am and the stable release of Firefox 14 is going to be out on Tuesday evening.
I’m currently using the 7th beta release of Firefox 14. It’s spent 6 weeks at nightly, 6 weeks at aurora and nearly 6 weeks at beta by the time I use it. I doubt there is much difference between a release candidate and what I’m on now.
Release candidates were more applicable when the rapid release cycle was new. Now that the process has matured and has gone through 9 releases, they’re obsolete. The first beta builds are now RC quality, with very few changes being made. I’ve used all the channels and the only one that exhibits stability/performance issues is Nightly. These days even Aurora builds are perfectly stable and fine for every day browsing.