Mozilla plans an orderly shift from raw new code to a polished final version of Firefox every 16 weeks.

A faster, regular release schedule isn't the only idea Mozilla is adopting from Google's browser. The organization also is embracing a plan to give Firefox a similar spectrum of test and stable versions to try to bring new features to market swiftly.

The general idea is to issue new versions of Firefox with varying levels of maturity, with the more mature versions geared for larger audiences, according to a draft document published by Mozilla programmer Rob Sayre.

The goal of the overall effort is to inject more competitiveness into a browser that deserves credit for reinvigorating a market left stagnant by the dominance of Microsoft's Internet Explorer. Firefox still is the No. 2 browser in worldwide usage, but now Google's Chrome has attracted many technophilic early adopters, and the brand-new IE9 gives Microsoft a competitive browser again.

The biggest risk coming with the new Firefox release philosophy is leaving behind the slower-moving users. Firefox has gained mainstream acceptance, but the fast-moving, auto-updating philosophy of software development can be at odds with, for example, conservative IT departments.

Mozilla plans a cascade of gradually maturing releases over a 16-week cycle.

Chrome comes in four or five flavors, depending on how you're counting. The most raw "nightly" version is built, well, nightly, to include the latest patches. The developer release is more settled down but still designed as a proving ground for new features. The beta release is where final testing takes place, and the stable release is for the mainstream market. In between the nightly and developer releases is the "Canary" version, but it's only for Windows, and it's updated irregularly. For example, it doesn't yet have the new Chrome logo that's in the developer release.

Mozilla is moving toward a similar model, but it uses different terms and doesn't have Canary. The draft document lays out placeholder version names of "mozilla-central (or 'nightly'), firefox-experimental, firefox-beta, and Firefox." Like Google, Mozilla calls the release mechanisms channels.

For now, Mozilla has just nightly builds, a sequence of beta and release-candidate releases, then the final version. The newest, Firefox 4, is due March 22, and under the faster schedule, versions 5, 6, and 7 are also due this year.

Here's how Mozilla describes the process to produce a new Firefox every 16 weeks:

Firefox uses a schedule-driven process, where releases take place at regular intervals. That means each release happens regardless of whether a given feature is ready, and releases are not delayed to wait for a feature to stabilize. The goal of the process is to provide regular improvements to users without disrupting longer term work...

The nightly channel gets new features as soon as they are ready, but it has the lowest stability of the four channels. The UI might change each day, and Web sites might not work at times. The firefox-experimental channel gets new features at regular intervals, but some of them might be disabled if it looks like they need more work. The beta channel receives only new features that are slated for the next Firefox release

The change comes with several consequences.

One big consequence of the new schedule is to security. Firefox users would need to embrace the constant updates, because old versions of Firefox won't be maintained..

"This proposal makes security updates occur along with Firefox releases, meaning we'll no longer be maintaining old branches," the document said. "Having security branches for each major update is untenable if we release as often as we aim to."

Another consequence is a move closer to the auto-update ethos that Chrome embodies.

"This proposal also requires changes to our software update behavior to make them happen more automatically in the background and interrupt the user less often. Otherwise, we will disrupt fx-beta users too much," the document said. "There will also need to be an option for users to completely disable automatic updates, so that they can manage their own upgrade process."

Mozilla plans to draw 500,000 experimental users and 1.5 million beta users from the existing beta-tester community.

The schedule is designed to produce a new Firefox version every 16 weeks, but because the beta channel feeds in more frequently, releases could theoretically come more rapidly. "Under this system, there is a choice to ship a general Firefox release at week 16 and every six weeks thereafter. That doesn't mean a release will happen every six weeks, but the option will be available," the document said.

Critical security fixes also could arrive independently of the regular schedule.