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Mozilla Firefox 4 review


The best all-round browser for power users, but still lags behind Google Chrome in terms of outright performance

Review Date: 23 Mar 2011

Reviewed By: Barry Collins

Price when reviewed: Free

Overall Rating
5 stars out of 6

Features & Design
6 stars out of 6

4 stars out of 6

Ease of Use
5 stars out of 6

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.

Author: Barry Collins

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User comments

Value for Money?

How does free software only get 4 out of 6 stars on the Value for Money rating?

By SteveSmith on 23 Mar 2011

Value for Money corrected

The Value for Money score was added in error. Now corrected.

Barry Collins

By Barry_Collins on 23 Mar 2011


It WAS there, and then it wasn't.. whoosh!

I imagined the conversation in the PC Pro offices after your comment surfaced..

Editor-in-chief: Have you seen this comment? Why did you give Firefox a 4 rating on Value for Money scale? It's free!

Reviewer: But.. it cost me £891!

Editor-in-chief: What!? Where did you get it??

Reviewer: From

By alvin on 23 Mar 2011

It's a very welcome update from 3. Jumplist support means I can get rid of winfox.

For some reason the Firefox button looks out of place. It looks too detached from the main browser. That's just me.

By james016 on 23 Mar 2011

I actually just came back here to see if I could remove my comment.
Afterall, it doesn't really matter if it has a VfM rating of 1 or 6. We all know that it's free.

It feels like commenting on bad punctuation or grammar in a post.

Oh well, too late now.

By SteveSmith on 23 Mar 2011


Performance definitely seems better than 3.x. I tried it on a circa 2004 Athlon 64 last night running XP and it was definitely snappier than the version it replaced.

By Rouleur on 23 Mar 2011

Am I the only one who will try and make FF resemble 3.x?

One reason I stuck with FF is because I liked the UI compared to chrome.

By tech3475 on 23 Mar 2011


I'm sure Barry Collins had a chuckle too, as I did, so free your conscience!

It was obviously an error but I appreciate the giggle all the same.

By alvin on 23 Mar 2011

hmm you peacemaker score seems low. I got a higher score, admittedly by only 200 points but I did this with 2 Visual Studios open, a SQL Server, OneNote, Outlook, 4 IE windows open and 9 tabs in Firefox 4 open.

By TimoGunt on 23 Mar 2011

tell a lie, it doesnt make any difference what you have running. I managed to get 4400 though

By TimoGunt on 23 Mar 2011

Wow and Chrome 10 gave me 9664. That's quite a big difference to your results

By TimoGunt on 23 Mar 2011

Benchmark scores

We ran the benchmarks multiple times on each browser and took an average.

Remember that the browsers are constantly updated in the background - especially Chrome - so variations can occur.

@Alvin - don't be silly. I've never paid for a web browser. I spend all my money on Linux OSes.

Barry Collins

By Barry_Collins on 23 Mar 2011

Looks pretty good so far. I find it quite well balanced in terms of minimalism. Chrome was too minimalistic. I really hope they now work on memory handling for the next updates. It does get quite annoying after sometime.

By isaac12345 on 23 Mar 2011


Why does FireFox still have a separate Google window when IE9 and Chrome both allow searching direct from the URL bar? Oddly, this sometimes works in FF but I often get a 'can not locate URL' message (or words to that effect).

By anthona on 23 Mar 2011

The future

Ok, the future is touch, which we all know and ie9 improves the Win7 support, but how does this browser perform?? Opera are working on a full touch version which sounds good, but where is it?

P.s. Currently own the excellent Asus EP121

By rhythm on 23 Mar 2011

App Tabs

What about app tabs you didn't mention this feature at all. None of the screenshots show it in use either. Running Gmail Twitter etc in this mode is brilliant. More details here

By Trash on 23 Mar 2011

Waiting till addon suport

It kind of annoying that you build up a small library of add ons and they bring out a new update that makes half of them incompatible. I still prefer my customized Firefox 3.6 than this new 4 one.

By GangstaNun on 23 Mar 2011

Yesterday I downloaded

Yesterday I downloaded, it took me a while to get used to. But I'm very happy.

By georgeUS on 24 Mar 2011

Norton And Mozilla Firefox 4

But what is neutralized me one of the options of Norton?

By georgeUS on 24 Mar 2011

One minor irritation... that they've stopped the browser from recognising the "TabMinWidth" option in about:config. Now you need an addon to lower the relatively high minimum tab width.

Sorry Mozilla, I'll take being able to view all my tabs simultaneously over a swanky scrolling mechanism any day for usability!

By Trippynet on 24 Mar 2011

peacemaker is a very bad idea if you want to compare browserspeed

Peacemaker is a very bad idea if you want to compare browserspeed (atleast the last time I checked).

The Peacemaker benchmark uses the browsers own timers/date/time functions of which the granularity differs among browsers.

So you can't use them to compare browsers.

if you have something running for 30ms in a browser and check the date time before and after it, one browser will tell you 24ms past and other way tell you 40ms.

That is not an environment that can be used to compare browsers.

By rgbstock on 24 Mar 2011


did you get the tabs to appear right at the top of the window like that? On my W7 system, the tabs appear on their own row under the orange "Firefox" button and I cannot find a setting to change that.

Not withstanding this, Firefox has the best minimalistic design for my money (at least once you have removed the now under-employed home and bookmarks buttons). The "Firefox" button is a brilliant idea since you can now strip the UI off altogether with out having to remember the 'alt' key trick to get the menu bar back. (Hint: to loose the tab bar when only one tab is open, un-check "Always show the tab bar" on "options" "tabs".)

Firefox looks like taking the default browser slot back from Chrome for me. IE9 is surprisingly good too, but that visually illiterate chopping off of the bottom of the back button would irritate the hell out of me. Does Microsoft not employ ANY designers?

By JohnAHind on 24 Mar 2011

tabs at the top of the window

@JohnAHind Maximize the window and you are done.

It is not an option or anything like that. I guess they just want to make it easier for users to drag the window if it isn't maximized.

And guessed that people that have their window maximized really do want the maximum amount of screen realestate for the webpage.

By rgbstock on 24 Mar 2011

"tabs now nestling neatly at the top of the window".

Oh no it doesn't. It is not a default or found in the standard FF4 option settings. It is customised by a script using the USER STYLE add-ons; couple that with AUTOHIDE NAVIGATION BAR the browser window is beautifully maximised.

By itchee on 24 Mar 2011

Opera 11 anyone?

Does it not seem to anyone else that all the other browsers are copying the style of Opera. Tabs at the top of the window, menu button in the top left hand corner instead lots of small menus. Increased performance etc..... it's all from Opera. Why was Opera not benchmarked alongside the others???

By Barff1706 on 24 Mar 2011

What about corporate support?

Still no support for role out in a corporate environment other than silent install but no help with configuration.

By Lorribot on 24 Mar 2011

Blurry text with Firefox 4

Am I the only one here to have a problem displaying text on Firefox 4?

Text appears smaller than I remember in FF3 and FF4 does a poor rendition of anti-aliasing, making text on most websites much harder to read.

By pedro_john on 25 Mar 2011

sence the upgrade I can only look at bookmarded webpages.

The search botton there but not working when pressed

and the some of the page is not desplaying correctly

but it working fine from my FF on a stick and another computer


By mprltd on 25 Mar 2011


Yes, I also wasted half an hour of my life making FF4 look like FF3. What on earth made them remove the status bar? Bonkers decision. You now have to install an extension to have a status bar... Worth it, though, FF4 is faster.

By john_dk on 25 Mar 2011

Where is that button?

I don't have a 'Firefox button' top left. Just the usual menu entries: File, Edit, etc.

So far I can find no reference to it in Options...

Terry, East Grinstead, UK

By terrypin2 on 25 Mar 2011

Where is that button?

Just untick the menu bar in Options Terry

By Trash on 25 Mar 2011

Opera sneaking up on Firefox

I really like Firefox 4... and I only made it feel a little like my old Firefox 3.x!

Out of curiosity I tried the Opera 11.1 Beta. It is faster and very 'customizable' too. I would have stayed with it except my copy got a little buggy on Win7 64 bit... I will try it again when the final is released.

By Kevin000 on 29 Mar 2011

... standards compliant ....

Funny ... TalkTalk webmail inbox stopped working when I upgraded to FF4.0. I guess either TT or FF is not compliant!
Incidentally, TT told me to go to a supported browser - a list which includes FF4.0 !!

By Dairs on 3 Apr 2011

Cookie Handling

Would like to change from IE but not while FF doesn't allow a prompt option for cookies. I mean, why not. Does it affect performance or is it that advertisers don't like it?

By StuartLaw1 on 15 May 2011

Cookie Handling!!!

FF does allow cookie prompting and has done since at least FF2 from memory. Just go to tools/options and select the privacy tab. Check the "accept cookies from sites" box and set the "keep until" drop down to "ask me every time".


By IANAT2 on 21 Jun 2011

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