For many people, the browser wars are all about one thing: speed. There's no doubt that version 3.5 of Firefox is significantly faster than version 3. Pages load noticeably more quickly for a number of reasons, not least because Mozilla built a new JavaScript engine called TraceMonkey for this version of Firefox.
How much faster is open to debate. Mozilla says it ran the industry-standard , which measures how quickly browsers render JavaScript, on versions 2, 3 and 3.5 of Firefox, and asserts that the newest version is and more than ten times as fast as Firefox 2 on the test. Other testers have .
Of course, rendering JavaScript quickly doesn't necessarily mean that all Web pages load faster. Microsoft, for example, argues that for most Web pages, other kinds of speed-ups are more important than rendering JavaScript quickly. I'll leave that debate to Microsoft, Mozilla and other browser makers. But putting aside any speeds-and-feeds specs, I can tell you that from the user experience, Firefox 3.5 is lightning fast -- it seems to me about comparable to the recently-released Safari 4.0 for the Mac.