Mozilla Firefox Will Become More Memory Efficient

Martin Brinkmann
Nov 7, 2011
Updated • Mar 15, 2012

The Mozilla Firefox web browser has quite the bad image when it comes to memory efficiency. You see claims all over the Internet that the browser is eating up more memory than other browsers. Comparisons often are not entirely fair to begin with, considering that most Firefox users have their fair share of add-ons installed in the browser which add to the browser's overall memory consumption.

With Firefox 8 being released the minutes we speak, it is time to look at the improvements that Mozilla has in store for Firefox users. I have already covered the planned changes of Firefox 9, and the big JavaScript performance boost of that version in detail.

More interesting in regards to the browser's memory efficiency and footprint are Firefox 10, or maybe Firefox 11. Firefox 10, which is currently available as a Nightly release (think of it as regularly released alpha versions that are not suitable for productive environments, may be the version of the browser that changes the user perception from a memory eating browser to a slim and efficient one.

Firefox developer Nicholas Nethercote some days ago detailed the changes that Mozilla has in store for the upcoming versions of the browser. According to Nicholas, the JavaScript engine is often the component of the browser that is "responsible for consuming the most memory".

What Nicholas describes then are pages of "programmers-talk" about how Mozilla intents to reduce the browser's footprint by optimizing various components and technologies of the browser's JavaScript engine.

Probably the biggest news here is the retirement of the JavaScript engine TraceMonkey which will reduce the browser's overall memory footprint and make the Firefox itself a smaller program. Jaegermonkey for the time being will become the only Just-In-Time compiler of Firefox. This again will change in the near future with the introduction of IonMonkey, a JIT compiler that is said to "generate code that is not only much faster, but much smaller".

Mozilla developers are furthermore experimenting with technologies that reduce the overall size of JavaScript compartments in the browser. Some of the improvements promise great memory reductions. Luke Wagner's proposition to reduce parts of scripts that are never run could reduce the "script-data" usage of the browser by up to 70%. Objects in SpiderMonkey, represented by JSObjects may see a size reduction of about 60%, while Shapes, another important data structure, will see optimizations that take them from 40 or 64 bytes to 24 or 40 bytes.

The majority of those memory optimizations will likely land in Firefox 10 or Firefox 11. Firefox users who now head over to the Nightly repository to download the latest Firefox 10 version right away will notice that the browser is not really showing any memory footprint improvements right now. Improving the browser's memory efficiency is a work in progress.

What's your take on browser memory consumption and speed? Is Firefox really that heavy on RAM usage?


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  1. FX10 said on November 12, 2011 at 10:16 am
    1. Martin Brinkmann said on November 12, 2011 at 10:56 am

      Thanks, noticed a issue with the add-on compatibility reporter:

  2. Dan said on November 11, 2011 at 1:57 pm

    Version 8 is using ~170 MB of RAM for one f***king tab and 1.2 GBs for 60 tabs – all with text and not special JS or AJAX or other stuff. I don’t know what to do – I need the addons, so I’ll keep using it, but please don’t say that it’s “more memory efficient”, because it’s been that way since version 4…

    Instead of running a virtual machine, I have to allocate ~1.5 GB to Firefox – just great… imagine if I had _only_ 4 GB of RAM…

    Besides, what’s with the version numbers – I remember when Firefox 3 used to be a huge improvement over 2, now it’s at version 9 and it’s just like 4 – it’s very confusing. Will we get version 20 by the end of 2012, because I’d love to see that :-)…

  3. FX9 said on November 11, 2011 at 2:24 am

    Firefox 9.0 Beta released for testing, includes Type Inference which increases performance by 30%.

    1. Martin Brinkmann said on November 11, 2011 at 11:00 am

      I mentioned it here:

      Cannot really say that I have seen a big different in day to day work.

  4. Dom said on November 7, 2011 at 10:58 pm

    From my observations, claims of Firefox bloat and big memory usage almost exclusively come from Chrome fanboys.
    Which is doubly funny, because Chrome uses about +50% or even more memory than Firefox, given the same amount of webpages loaded and extensions in use, and it’s been that way since the very start. IE9 comes close to Chrome in that regard. Just because the total memory footprint is somewhat harder to grasp at first glance in Task Manager, because each tab/extension runs as separate process vs single large process of Firefox/Opera, doesn’t mean everyone is too stupid to add all of them up, or lacking common sense to understand that such level of isolation requires significant amount of overhead and that speed/responsiveness of their browser doesn’t just happen by magic (newer Webkit design comes with much more liberal use of RAM and less disk I/O, compared to older Gecko which was built back when RAM was much more expensive).

  5. Dougle said on November 7, 2011 at 10:51 pm

    The biggest single factor ‘affecting’ memory/start-up, with virtually any browser, is the inclusion of addons/extensions, which I personally have no problem with, as I’d rather incur a small penalty, in terms of resource utilisation, for the functionality I require.

    For a long time now, I’ve used minefield/nightly (nightly x64 currently) builds of fx with multiple profiles. My standard profile has all the add-ons I want, which currently stands at 31. If I load this profile and open 10 tabs, memory utilisation is around 400MB. If I load another profile with no add-ons but the same 10 tabs, memory is around 220MB, which is slightly less than Chromium 17 and Opera 11.52 and slightly more than IE9 for the same tabs.

  6. Q said on November 7, 2011 at 9:45 pm

    I had started significantly using Firefox at version 3.6.15. I began maintain customizations (userChrome.css and prefs.js and an extensions) for the Firefox 3.6 series browser.

    I had later begun to use and maintain customizations for Mozilla Firefox 6 series browsers.

    I suppress the showing of tab related items, except for options to toggle preferences, from the Firefox user interface and set the preferences to disable opening in tabs as much as possible without using an extension to modify behavior.

    I had tested Mozilla Firefox 7.0.1 (including memory usage), but rejected it after finding that it performed less efficiently than the Firefox 6.0.2. All testing was performed on Windows XP Professional with Service Pack 2; the “Windows Classic style” OS visual style was used and the theme service was disabled.

    I had compared measured memory usage of the Mozilla Firefox web browser without extensions installed. I had tried to use a memory light test page and used “” as the browser start page and test page. At the time, “” did not have elements that should require much memory.

    I do not have the exact figures at the moment; however, I can give some more general information about my test results. Mozilla Firefox 3.6.23 series browsers used about 35 MB for the test page, Mozilla Firefox 6.0.2 used about 49 MB, and Mozilla Firefox 7.0.1 used about 52 MB.

    Mozilla Firefox 6.0.2 and Mozilla Firefox 7.0.1 started up much faster (especially cold start) than Mozilla Firefox 3.6.23.

    As an additional note, I suspect that much of the stability and memory management issues that Firefox has had in the past are related to the use and management of browser tabs; After disabling the use of tabs as much as possible I had found Firefox to be quite stable in its performance and typical memory management. The browser also does not seem to ever crash when tabs are not used.

  7. Xmetal said on November 7, 2011 at 9:22 pm

    I have say that I agree with Matt …. I have not sat down and looked at “exactly how much RAM” it is consuming; however, I did noticed performance wise 4.x seemed to be “slower” (I am a major FF Fan, by the way) the 3.x … with each release it seems to have gotten better and the main issue I have with FF is that (RAM consumption wise) … it still could be improved … to hear that is one of the things Mozilla is working on for Further releases .. is great news … I still (though i dont hate it) am not a fan of Chrome/Chromium .. seems faster than Firefox but I do not have 1/2 the addons for Chrome as I do for Firefox (that obviously slows it down compared to Firefox with NO addons at all) …… I rather wait a few extra seconds and have Firefox load.


  8. Matt said on November 7, 2011 at 8:19 pm

    I always look forward to reading Nicholas Nethercote’s updates, even if I only understand about half of what he writes.

    On RAM consumption: my experience was that it clearly took a turn for the worse with Firefox 4, but it’s become more and more efficient with each release since. Seven seems as stable in terms of RAM usage as 3.6 was. It’s looking like 8, 9, and so on will gradually improve on that.

  9. rob said on November 7, 2011 at 7:11 pm

    still no love for those with 64-bit systems?

    1. Martin Brinkmann said on November 7, 2011 at 7:14 pm

      Latest news is that they will finally support 64-bit when Firefox 10 comes out.

      1. rob said on November 8, 2011 at 4:18 pm

        oh my, i’ve been a fan of pale moon for a while but just tried waterfox and it’s the bomb! thanks

      2. Dougle said on November 8, 2011 at 9:49 am

        64 bit builds have been available for Windows Nightly for quite a long time, you can get them from the mozilla ftp or

      3. Ahmad Saleem said on November 8, 2011 at 9:38 am

        Source please?
        I am following FF since FF6 Nightly to FF10 Nightly and I never heard of any developer to support 64-bit on Windows early. It will be half baked browser.

      4. Nilpohc said on November 7, 2011 at 10:16 pm


        For an early 64bit support – on Windows – you can use Palemoon ( ) or Waterfox ( ). The first one used to be my favorite Firefox flavour on both 32bit and 64bit architectures because of its optimized and portable builds. I hardly tried the latter which however seems to work just fine after installation.

  10. Midnight said on November 7, 2011 at 7:00 pm

    Downloaded Firefox 8 from the Mozilla FTP site on Sunday and it works just peachy, as always!!

    Looking forward to further releases, which will/should show some serious improvements.

    Keep us in the look, Martin. Much appreciated! :)

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