I feel I should clarify a few things about the new release schedule. Many people are saying Mozilla is moving too fast with Firefox releases. It may appear that way because of the numbering change but things are not changing that much. In the past Mozilla would release an incremental update (such as 3.6.1) which included bug patches and minor security fixes about once every six weeks. A major release (such as 2.0, 3.0, 3.5, 4.0) about every six to twelve months. Further, with these major releases they would try to implement all the new features/improvements/enhancements at once. The problem with this method as seen in Firefox 4 was the browser was in development for nearly 18-months because they were trying to get everything working. Further, while it was still in development they would have to go back and make fixes for 3.5/3.6, push out an update then get back to working full time on Firefox 4.
To prevent this Mozilla is switching to this 18-week release plan. These releases are going to include bug patches and non-major security fixes that would normally be in an incremental update along with a couple new features. These are features which were planned for the prior release, but missed the development cut-off time. This allows Mozilla to get the new and updated versions of Firefox out when promised. If something is not ready, it is held back for the next release in 18-weeks. Also, what’s nice about this approach is new features/enhancements/improvements are introduced a couple at a time, instead of all being lumped into one release (such as Firefox 4) which can overwhelm users and also unknowingly cause stability issues.
Again, the biggest change is the numbering. We are going to see far less sub version numbering. For example Firefox 3.6 is currently at 3.6.17 and Firefox 4 is at 4.0.1. Very doubtful there will be a Firefox 4.0.2. This is going to make is a lot easier to know if people are running the most current version. Example someone will say they are running Firefox 3.6, but they could be running anything between 3.6.1 and 3.6.17, which makes a difference for troubleshooting. If they say they are running Firefox 4 we know it is either 4.0 or 4.0.1 and really is not that much of a difference between those two versions other than some minor patches. Also by going up whole numbers, this is going to eliminate a lot of confusion as well. Many times users say they are running Firefox 3.5 when in fact they are actually running 3.6 (or the other way around).
One more thing to keep in mind, it may seem like Firefox 5 is coming out fairly rapidly. This is true as Firefox 5 is on a 13-week (from the release of Firefox 4) schedule. However, work had begun on Firefox 5 several weeks prior to the finial release of Firefox 4 (Mozilla had some stability issues in Firefox 4 they had to work out in the few weeks prior to its release) so that is why this one is going to be out a little sooner. Firefox 6 will be on a true 18-week release schedule.