Mozilla Firefox 4 review

Mozilla claims it’s “leading the Web towards a universal standard” with its Do Not Track feature, but the majority of websites currently fail to recognise the system. Indeed, Mozilla admits “users will not notice any difference in their browsing experience until sites and advertisers start to respond to the header”.

Thus in our tests, a quick browse of travel websites led to a subsequent barrage of holiday banner offers on proceeding news sites. Mozilla admits it’s adopting a “chicken and egg” approach, but we can’t help feeling that a more pragmatic solution would benefit users, at least in the short term.


Sluggish start-up times and a reputation for gobbling memory when running multiple tabs sent many Firefox users running into the arms of Google Chrome. Does Firefox 4 address either of these weaknesses? Not judging by our tests.

Firefox is still disappointingly inefficient at handing back memory. With five tabs open the browser chomped through 104MB of RAM in our tests – significantly less than either IE9 or Chrome – yet yielded only about 35MB of that when we closed all but the Google homepage. Both Chrome and IE9 are much more effective at releasing RAM when tabs are closed, so if you use a lot of tabs you’ll still find the need to close Firefox down every so often to start from scratch.

And while Chrome patches are applied so discreetly that you often don’t realise the browser has been updated until a new feature appears in the menus, Firefox 4 continues to apply updates before you can get on with your browsing.

Firefox 4 is a mixed bag when it comes to browser benchmarks. It was marginally faster than Chrome in the SunSpider JavaScript test, but way off the pace in the more strenuous Futuremark Peacekeeper browser benchmark. Make what you will of Firefox recording an emphatic victory in Mozilla’s own benchmark suite, although it was significantly faster than IE in the Google V8 benchmark.

Firefox 4 v IE9 v Chrome

(Click graph to enlarge)

Standards and compatibility

The open-source Mozilla has always bent over backwards to be standards compliant, and Firefox 4 remains steadfast in its support for open standards. It scores a near-perfect 97 out of 100 in the Acid3 Test and supports many of the new HTML5 and CSS3 features, such as plugin-free web video, the new web forms API, and CSS transitions.

In the ongoing battle over web video standards, Mozilla has thrown its weight behind Google’s WebM format, although a Microsoft-published plugin offers support for H.264.

When it comes to operating system support, Mozilla is second to none. Not only does it offer Mac and Linux versions of the browser, its Windows support also stretches down to XP – something that Microsoft has conspicuously failed to do with Internet Explorer 9.


The new versions are done and dusted, and the bad news for Microsoft is that you still have to look beyond Internet Explorer if you want the best browsing experience. That leaves you with an enviable choice: Google Chrome if outright speed and performance are a priority, or Firefox 4 if a more fully featured browser is what’s called for.

The latter’s new additions such as Sync and Tab Groups are a boon for power users, while the revamped interface is a welcome improvement on the dated-looking Firefox 3.6. With Firefox’s unparalleled library of add-ons to back it up, it runs Chrome extremely close for the best overall browser crown.


Software subcategoryWeb browser

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