Firefox 5 is safely out the door, but Mozilla isn't resting, it's got both Firefox 6 and Firefox 7 baking at this very moment. Right now, Firefox 6 is in the Aurora channel and Firefox 7 is getting nightly releases, but it will be a couple of weeks more before they are being graduated, to the Beta and the Aurora channel respectively.
Mozilla has announce that it will still be two more weeks before we see a Firefox 6 Beta, on July 5 if everything goes according to plan. That's when Firefox 7 will enter the Aurora channel as well.
"The [Firefox 6] Aurora channel has seen a half dozen polish and stability fixes in the last week. There are about 30 approved for Aurora but not yet landed patches right now. If you own one of these, please get it landed or risk losing the approval. Aurora migrates to Beta in two weeks! Yes, Firefox 6 is very nearly done," Mozilla said in its weekly engineering newsletter
"[Firefox 7] mozilla-central continues to fly forward at a blistering pace with 415 changesets landed in just the last week (1450 changesets since the cycle began.)," it added.
"We are two weeks from the migration to Aurora (July 5th) so if you’re trying to make the Firefox 7 train, you’re gonna want to get on the stick," it warned.
This situation is unique, normally, all three, or four channels depending on how you look at it, will have a Firefox version at different stages of development. However, the delay is because Firefox 5 was pushed faster than the regular release cycle, to get the ball rolling so to speak.
"The [Firefox 5] Beta channel is currently resting. Because Firefox 5 was a shorter than (the new) normal cycle, we’ve got two weeks before the next uplift from Aurora. In the future, all migrations will happen on the same day," Mozilla explained.
When everything will moving at the regular pace, Firefox 5 will be in the stable or 'release' channel, Firefox 6 in Beta, Firefox 7 in Aurora and Firefox 8 (yes eight) will be in the mozilla-central repositories for nightly builds.