Firefox 4's first beta is 27 per cent faster than Mozilla's more stable browser, Firefox 3.6.6, but still lags behind rivals including Chrome, Opera and Safari, benchmark tests show.

According to tests run by Computerworld, Firefox 4 Beta 1 gained significant performance ground over its predecessor, yet still has a long way to go to catch the leaders.

Mozilla implicitly recognized that Tuesday when it launched Firefox 4's first general public preview . "This is just the beginning for performance improvements in Firefox 4," said Mike Beltzner, director of Firefox, in an entry on the Mozilla blog earlier this week .

Computerworld ran the SunSpider JavaScript benchmark suite in Windows Vista Business three times for each browser , then averaged the scores.

Apple 's Safari 5 remained the speed champ, but just barely: The Windows version of Safari was only 2% faster than Opera Software's flagship desktop browser, Opera. Last month, Safari 5 dethroned Opera , which had held the crown since February.

Firefox 4 beta

Opera 10.60, which landed last week, was nearly neck-and-neck with Safari, a better showing than in early June when Safari proved 9 per cent faster than the older Opera 10.53 on Windows.

Google 's Chrome 5, meanwhile, was 40% faster than Firefox 4, but slower than either Opera or Safari, putting it in the middle of the pack.

Computerworld used the "stable" build of Chrome 5 in the JavaScript speed tests, but also tested the current "beta" channel version of Google's browser. There was virtually no difference between the two on the SunSpider results.

Internet Explorer 8 (IE8), Microsoft 's newest production browser, was also tested, but remained the slowest by far. For all intents and purposes, IE8 isn't even in the JavaScript race.

Microsoft figures to pick up the pace with IE9, the version that's been released only in rough developer preview formats so far. The company has not announced a beta ship date, much less a final launch timetable, but a recently leaked presentation touting Windows 8 , the next version of Microsoft's desktop operating system, claimed that IE9 will shift into public beta next month .

Firefox may not be the fastest browser, but it's still the second-most-popular browser on the planet. In June, Firefox accounted for 23.8 per cent of all browsers used to reach sites monitored by Web analytics firm Net Applications. Internet Explorer gained ground at a record pace, which is highly unusual, to end the month at 60.3%. Chrome, Safari and Opera held usage shares of 7.2 per cent, 4.9 per cent and 2.3 per cent, respectively.

However, Mozilla has lost share in five of the last seven months since peaking in November 2009.

Firefox 4 Beta 1 can be downloaded for Windows, Mac and Linux from Mozilla's site. At the moment, only an English-language version is available.

Firefox 4 Beta 1 is 27% faster than the more stable 3.6.6, but can't match the speeds of Chrome, Safari or Opera. Smaller results are better. IE8 is not shown.