Mozilla has released the first Aurora build of Firefox 5,  Alpha 2 on April 12th. Firefox 5 is the first release being done under Mozilla’s new aggressive development plan.  Here is how the plan works, there are 4 stages or development channels each approximately 6-weeks each with a total of 18-weeks from Nightly to Release:
Nightly (Weeks 1-6) – the freshest (and sometimes unstable) developmental builds new features will be introduced during this cycle. Since Firefox 5 has moved to Aurora, Firefox 6 is now in the Nightly cycle.
Aurora (Weeks 6-12) – all new features for this new version have been landed. This is more of a ‘developer preview’ and again may not be the most stable.  If the new feature has not already been approved by this time, it will be added in the current nightly (in this case Firefox 6).  Some features may be cut if they can not be made to work during this six week cycle (in which case they will be kept in the Aurora channel for Firefox 6). Firefox 5 is now currently in Aurora and there will be ‘nightly’ releases on the Aurora channel as well. If a feature is still not working correctly at this point it will be yanked for this release and placed on the Aurora of the next release. In this case should something like this happen with Firefox the feature will be slated for Firefox 6. The rule now is, if it is not ready, it is not going to be in this release (this happened way too much with Firefox 4 which was why it was so delayed).
Beta (Weeks 12-18)- during this cycle any problems, issues, etc that came up during the Aurora cycle will be fixed. During this time the Release Candidate builds will be released.
Release (Week 18) – The final release of the new Firefox version.
Here is an approximate time table of Firefox 5 as it moves through the channels (keep in mind Mozilla is running a shorter development cycle on Firefox 5 of about 13 weeks):
Nightly (labeled as Firefox 4.2a1pre) – March 23, 2011
Aurora (labeled as Firefox 5.0a2) – April 13, 2011
Beta (will be labeled as Firefox 5.0b#) – May 17, 2011
Release – June 21, 2011
So right now there is nothing in the beta channel. Come around May 17th, Firefox 5 will move to the Beta channel. Then Firefox 6 will move to the Aurora channel. At this time Firefox 7 will be introduced into the Nightly channel. I have added a new widget called Firefox Development Channels that will show what is in each channel. I’ve also updated the main site showing the current release/development status of Firefox 3.6, 4.0, 5.0 and 6.0.
Download : Via Mozilla