Mozilla has pushed back the planned Firefox 4 release to 2011, a delay that's no surprise given the difficulties in releasing the first full-featured beta of the open-source browser--but that also gives breathing room for several competitors.

Mozilla had hoped to release Firefox 4 in 2010, but a newly updated Firefox 4 schedule shows the first release candidate arriving in early 2011.

"Development on Firefox 4 has not slowed down, and strong progress is being made daily. However, based on the delays in completing the 'feature complete' Beta 7 milestone against which our add-on developers and third-party software developers can develop, as well as considering the amount of work remaining to prepare Firefox 4 for final release, we have revised our beta and release candidate schedule," said Mike Beltzner, vice president of engineering for Firefox, in a mailing list message yesterday. "The frequent beta releases have been extremely helpful in identifying compatibility issues with existing web content, so we plan on continuing to release beta milestones through the end of December. Our estimate is now that release candidate builds will ship in early 2011, with a final release date close behind."

Six beta versions have arrived in recent weeks, but Firefox 4 beta 7 hasn't appeared, despite more than six weeks of frenzied development. One big issue holding up release has been the integration of Firefox's older Tracemonkey engine for running Web-based JavaScript programs and the new JaegerMonkey engine that draws on Google's V8 engine in Chrome.

Mozilla's arewefastyet.com site shows progress matching Safari and Chrome JavaScript execution speed, but new JavaScript engines can be tough to tune. Several JavaScript bugs are blocking Firefox 4 beta 7.

The JaegerMonkey JavaScript engine in Firefox 4, whose performance is shown here in purple, has proven competitive against the engines in Apple&39's Safari and Google&39's Chrome, as measured by the SunSpider and V8 benchmark suites. (Click to enlarge.)

Among other changes in Firefox 4 are a revamped interface, a Bing search option, hardware-accelerated graphics, the new Jetpack foundation for add-ons to customize the browser, an HTML5 parser to interpret Web pages with the new standard for creating them, and WebGL for 3D Web graphics.

And presenting a major new front in the browser wars, Firefox 4 also works on Google's Android operating system for phones and other mobile devices. Today, the cutting edge in that market is dominated by the WebKit engine used on Android, Apple's iOS, and several other mobile operating systems.

Releasing the new version is important for Mozilla. Firefox remains the second most popular browser as measured by Net Applications usage statistics, but the browser market hasn't been as competitive as it is now in more than a decade.

Firefox and Opera kept the independent-browser fires burning during the years when Microsoft's Internet Explorer was dominant but somewhat dormant after its victory in the first browser wars of the 1990s.

In September&39's browser usage, IE dipped back below 60 percent share and Chrome gained 0.5 percentage points of usage.

Web technologies started picking up steam again, with Apple's Safari engineers joining the development effort begun by Opera and Firefox, and Firefox started wrenching significant share away from IE. But in the last two years, Google Chrome burst onto the scene, rising rapidly to third place and flattening Firefox's growth.

And even more recently, Microsoft began fighting back again with IE9, currently released in a first beta version. This browser was developed more in the open, letting outside developers get more of a say in its workings, and features many new modern abilities. Perhaps chief among them is ambitious hardware acceleration.

Firefox 4 has hardware acceleration, too, and unlike IE9 offers it for Mac OS X, Linux, and most important the vast number of Windows XP systems still in use.

Firefox 4 beta 1 for Android was powerful enough to run the full JavaScript-intense desktop version of Gmail, including the priority inbox. However, in this case, the Web application fell back to its more basic HTML interface.