Alongside these developer-friendly upgrades there's a predictable focus on wider web technologies, with both HTML5 and CSS3 support improved from previous versions of Firefox. Where html5test.com gave Firefox 3.6.6 (the current version at the time of writing) just 139 points out 300 for its feature support, Firefox 4 beta 1 now raises that score to 199 - with nine bonus points for its support for the WebGL 3D graphics interface. It's still neck and neck with Chrome, which scored 197 points, and behind Safari on 207; but we're definitely getting there.
Meanwhile, in the Acid3 CSS test the new beta scored 97/100, up from 94/100 for the current version. Again, though, it's not the front-runner: Safari, Chrome and Opera all scored full marks.
And it's a similar story with performance. Firefox 4 introduces the new Gecko 2 layout engine and a tweaked JavaScript interpreter, but you probably won't notice any improvement outside of a synthetic benchmark. On our test system (based on an Intel Core i5-750 processor) the new beta completed the SunSpider JavaScript benchmark in an average time of 0.79 seconds, compared with 0.93 seconds for version 3.6.6. If JavaScript performance is important to you, you'd get a much greater speed boost by switching to Chrome (0.38 seconds) or Opera (0.36 seconds).
From beta to final release
Of course, this is only a beta, and if you've any strong views on the way Firefox 4 beta 1 works you can hit the "Feedback" button and share them with the developers. But the beta already feels polished and complete, so it's reasonable to assume the final release will probably be very similar to what we have now.
On that basis, Firefox 4 will be an improvement on 3.6, but hardly a game-changer. It brings no unique killer feature, nor a big enough performance boost, to set it apart from the other "alternative" browsers. Then again, it still feels fast and usable, and enjoys not only a huge library of add-ins but now a very simple framework for developing new extensions and web applications. If that's valuable to you, this could be a very attractive upgrade.
Verdict
With a new look and some clever upgrades under the bonnet, Firefox 4 promises to be a worthwhile update.
But it’s developers who’ll benefit most: there’s not much here to excite IT managers or casual users.
