Mozilla is currently planning a truncated schedule for Firefox 5, which should ship June 21. To meet that deadline, Firefox 5 has to hit the "aurora" channel April 12 and reach beta by May 17.

With Firefox 5 done, Mozilla will shift to a standard 18-week schedule that will put Firefox 6's release around mid-August.

To meet those dates, Mozilla will add features to Firefox as it goes. If a feature is not ready for the first of the four channels -- what the company calls "nightlies" as well as "Mozilla central" -- it will not be added later to the aurora or beta builds. Features with problems will be backed out of an edition -- say Firefox 5 -- and deferred until the next in line.

Google essentially does the same with Chrome.

Mozilla will apparently also stop shipping interim security updates as of Firefox 5, and instead patch vulnerabilities as fixes are crafted, with the final Firefox build given priority.