Firefox, as you probably know is on a faster release schedule and Firefox 5 is already in beta. According to Mozilla's release schedule, you should expect the release channel to get the stable version of Firefox 5 in less than a week now.Mozilla's Firefox Facebook Page is already foreshadowing the release of the next stable version of Firefox.
Also, according to the release schedule, Firefox 6 will drop from the Aurora channel to Beta.
As for Firefox 5, you should probably not expect big features. I am using the Firefox 5 Beta and there's not a big difference from Firefox 4. It has no identity management, no inbuilt PDF reader and not even a UI refresh.
