According to tests run by Computerworld , Firefox 3.6, which Mozilla , is the third fastest of five Windows browsers tested. Firefox renders JavaScript three times faster than Opera 10 and more than four times faster than 's Internet Explorer 8 (IE8). It's also 14.5% faster than Firefox 3.5, the Mozilla browser that debuted in June 2009, a slightly larger speed increase than Mozilla has claimed.

But even with the JavaScript speed boost, Firefox 3.6 can't match Safari or Chrome. Safari is twice as fast -- and Chrome 4.0 nearly twice as fast -- as Firefox.

Safari edged Chrome for first place in the speed race, beating 's browser by about 6.5%, a slightly smaller lead than in a November time trial that of the browsers against each other.

Computerworld ran the SunSpider JavaScript benchmark suite in Windows XP Service Pack 3 (SP3) three times for each browser, then averaged the scores to arrive at the final rankings.

Most browser makers have been aggressively promoting improved JavaScript performance for nearly two years now, dating to when Mozilla began touting the performance boost its gave to what eventually was tagged as Firefox 3.5 and .