I'm not sure what the article means by "ahead of schedule". The release date was set months ago, and new versions are always released a few days early via the Mozilla FTP servers.
Firefox 5 isn't a huge release, and there won't be nearly as much fanfare as there was with 4. The point of Firefox 5 is to switch over to the "train" model. The train leaves four times a year, no matter what-- and if a feature doesn't make the train, it has to catch the next train. There is no waiting for a feature.
Incrementing by one each release (rather than 4.1, etc) may seem like Mozilla is making a big deal out of nothing, for the sake of publicity. However, it just means that all releases are equal. There will never be a huge 3.6 => 4 style release ever again, and eventually people will lose track of what Firefox version they have (much like how people have lost track of Chrome versions).
tl;dr: While it has a few cool new features, Firefox 5 is more to get Mozilla in the release-often groove.
1. Upgrades will be downloaded in the background and installed automatically by default. It's not yet as seamless as Chrome, though it's moving that direction. (For example, a while after the upgrade is downloaded, current versions of Firefox will prompt you to restart, with a dialog which is a bit more intrusive than the tiny "Christmas tree" toolbar icon that Chrome uses.)
2. Updates will be automatic by default. They'll be installed without prompting, unless users disable auto-updating. This is important because, just like Chrome, the updates will include security fixes.
Firefox 5 isn't a huge release, and there won't be nearly as much fanfare as there was with 4. The point of Firefox 5 is to switch over to the "train" model. The train leaves four times a year, no matter what-- and if a feature doesn't make the train, it has to catch the next train. There is no waiting for a feature.
Incrementing by one each release (rather than 4.1, etc) may seem like Mozilla is making a big deal out of nothing, for the sake of publicity. However, it just means that all releases are equal. There will never be a huge 3.6 => 4 style release ever again, and eventually people will lose track of what Firefox version they have (much like how people have lost track of Chrome versions).
tl;dr: While it has a few cool new features, Firefox 5 is more to get Mozilla in the release-often groove.