While it doesn't stand out dramatically from its predecessor, the new version does bring Firefox closer to the cutting edge of Web standards, and offers a handful of clever innovations in privacy that its rivals would do well to steal for themselves. But the browser's much-ballyhooed claims of a big speed boost aren't all they're cracked up to be.

On its Web site, Mozilla touts version 3.5 as "the fastest Firefox ever." But that claim refers solely to its new TraceMonkey JavaScript engine, which handles many of the Web's interactive elements, but not the fundamental rendering of HTML code. Its assertion that Firefox 3.5 is more than twice as fast as its predecessor here is true--but Mozilla doesn't elaborate on how the new version compares to rivals. And while its JavaScript performance has definitely improved from 3.0, Firefox 3.5's speed in other areas actually seems to have decreased.

Mozilla bases its speed-boost claims on results from the SunSpider JavaScript Benchmark. My own SunSpider tests, on a 2GHZ aluminum MacBook with 2GB of RAM, roughly matched Mozilla's results. Firefox 3.0.10 completed the test in 3,645.8 milliseconds, while Firefox 3.5 roared past it in 1,464.4 milliseconds. But Mozilla understandably does not mention that Apple's rival ( Macworld rated 4.5 out of 5 mice ) browser could soundly thump both of them in the same test, clocking in at 756.4 milliseconds--nearly twice as fast as Firefox 3.5.

Safari 4 also bested Firefox 3.5 in the XHTML and CSS rendering tests I ran--but surprisingly, so did Firefox 3.0. Firefox 3.5 displayed a local copy of the XHTML test file in 2.66 seconds, compared to 2.55 seconds for Firefox 3.0 and 0.49 seconds for Safari 4. In CSS rendering, Firefox 3.5 took 361 milliseconds to complete the same locally hosted test that took Firefox 3.0 355 milliseconds, and Safari 4 just 35 milliseconds.