Mozilla has launched Firefox 5, a new version of the popular open source Web browser. This is the first update that Mozilla has issued since adopting a new release management strategy that has drastically shortened the Firefox development cycle.

Mozilla introduced its ambitious 2011 roadmap in February, with a plan for delivering four major releases during the year. A draft of the new release management strategy was unveiled in March, before Firefox 4 was released. As we pointed out at the time, the new approach is a radical departure from how Firefox has traditionally been developed: Mozilla has historically issued only one major release a year.

Despite the significant challenge of increasing the Firefox release cadence, Mozilla has successfully delivered Firefox 5 to users a mere three months after the release of Firefox 4. The new version is unsurprisingly light on user-facing changes due to the shortened cycle, but has some decent improvements under the hood. It also proved to be fairly robust during our tests, which suggests that the browser's quality hasn't suffered from the transition to the new release management strategy.

The most significant improvement in Firefox 5 is the addition of support for CSS animations, an experimental CSS3 feature that allows Web developers to do keyframe-style animation on CSS properties. Because the underlying standard hasn't been finalized yet, Mozilla's implementation uses the -moz browser vendor prefix.

Another noticeable change is that the checkbox for toggling the Do Not Track (DNT) header has been moved to the Privacy tab of the browser's preference dialog. Mozilla introduced the option for enabling the DNT header in Firefox 4 even though the header was recognized by virtually no advertisers at the time. That proved to be a sound move and has helped accelerate adoption among advertisers and other browser vendors.

Now that the header is starting to gain industry acceptance, Mozilla is making Firefox's DNT checkbox more discoverable by moving it from the Advanced tab of the preferences dialog to the Privacy tab. The DNT option has also been added to the Android version of Firefox, which was released concurrently with the new desktop version.

Aside from these minor user interface changes and new features, Firefox 5 brings a number of bugfixes and performance improvements that will improve the browsing experience.

Although the changes in Firefox 5 don't seem like much, they illustrate some of the advantages of a shorter development cycle. Mozilla will be able to roll out support for emerging Web standards at a faster pace, making it easier for Web developers to take advantage of the latest and greatest capabilities that the Web has to offer. It will also shorten the time window for rolling out optimizations and other similar enhancements that directly benefit regular end users.

One downside of the shorter development cycles is that third-party developers have a lot less time to update their Firefox add-ons for compatibility. We tested a bunch of popular add-ons with version 5 and didn't haven much trouble.

Mozilla is already hard at work on Firefox 6, the next update on the roadmap. The new version is expected to bring back WebSockets and add support for Server-Sent Events and the HTML progress element. We are really hoping to see full multiprocess browsing in Firefox 7 later this year, but it's not clear yet if that will happen.

Users can obtain Firefox 5 by running a browser update or downloading the new version from the Mozilla website. For additional details, you can refer to the official release announcement.

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