Neil Turner's Blog

Blogging about technology and randomness since 2002

Firefox and Memory

A lot has been said about Firefox and its memory usage. Some report no problems with Firefox, and that it behaves well and doesn’t hog their system. Others bring tales of woe about how Firefox has brought their system to its knees by hogging all the available memory and CPU.

My systems fall in to the former category. Firefox, on my system, seems to work pretty well, and this is using the default memory management settings. It almost never needs more than 80 MB of memory and makes comparatively conservative use of virtual memory too. CPU can be a bit high while big pages are loading, but otherwise it’s pretty well-behaved. It even uses less memory than IE7 Beta 2 (which Fred Langa claims should be the opposite).

But I’ve also seen some systems where Firefox’s memory usage grows and grows, and after a couple of hours it has hogged 300 MB of memory and is using some or all of the CPU, even when idle. This is still prevalent, even on Firefox 1.5. Scot Finnie goes over some of this in a Computerworld article.
Mozilla are aware of the issues and have been working to try and cure any memory leaks that may be occurring – several patches have been checked in as a result and these should hopefully make it into Firefox 2.0 or 3.0. But Firefox’s memory problem is a difficult one to tackle, because the browser is so customisable. Every copy of Firefox is used in a different way, so in tracking down memory leaks it’s fair to say that Mozilla have their work cut out.

Some web sites, especially those with lots of JavaScript in them or that have especially big pages with lots of images, do require more memory to load and display, than simple, short, text-only pages. So if you regularly browse the former and not the latter then Firefox’s memory usage is bound to be higher. It’s also affected by what browser plugins are used – QuickTime and Adobe Reader especially use up a fair bit of memory that isn’t necessarily released when you navigate away from a page, so users of multimedia sites can also expect higher memory usage.

Firefox’s ability to be expanded using extensions also creates another variable – some extensions will also put more strain on memory. There are also those which are quite CPU intensive.

And everybody’s computer is different – from the hardware to the operating system to the programs it runs. Some computers, like my laptop, run Firefox fine. Others may have major problems, simply because of how they’ve been set up. And remember that in Windows Firefox has two distinct disadvantages against Internet Explorer – it’s not built into the operating system like IE is and is designed to be easily portable to other platforms, which usually makes the code less efficient.

So to say that Firefox is a memory hog isn’t entirely fair. Sure, for some it is one, but for others it’s not.


  1. I am one of the lucky ones who had it both ways. Firefox has always worked fine on my home computer, a laptop running XP home. Until recently, my work computer (a desktop running Windows 2000) would choke and die horribly after about five minutes of Firefox use. I had installed it of my own accord (technically a no-no where I work), so I figured something had gone wrong – but I loved Firefox so much that I put up with it. Recently, I was upgraded to XP Professional at work. When I noticed Netscape 7 had gone away (it was installed by default when I had Win2K), I called the helpdesk and asked if I could please be given either Netscape or Firefox. When the tech came, he gave me a choice; I chose Firefox and have been working just fine since.
    So I’ve no idea what the difference was, but I got to experience both sides of this coin.

  2. hmm in my case firefox works just fine though i did notice that some plugins including adobe reader can tend to slow it down horribly and thats when it start to over hog memory… heavy plugins aren’t handled too badly byit but it could be improved i imagine

  3. At work we have some really really old laptops we use in vehicles. We like to get old ones because they’re just $100 or $200. I’ve managed to install a minimal version of XP on them that only takes a few hundred megs of HD space and 48 megs of memory. This allows the machine to function on 128 megs of ram.
    The low ram usage makes a good low-memory browser important. Our intranet/vpn server uses a lot of AJAX-type technology so a MODERN browser is required to.
    So far, Firefox has been working well but I do look forward to smaller memory profiles.
    Thank you for all your hard work!

  4. I was just about to post about this – well, in a completely different way ;-).
    FF on this WinXP Pro machine is excellent. Upstairs on the (admittedly ageing) Win2K machine it’s gotten to be an absolute nightmare since 1.5 or so. [The same extensions are installed on both.)
    It’s so bad on the Win2K machine that I’ve started using Opera instead – no bad thing! But I do miss my lovely Firefox so if you hear of any news on this I’d be glad to hear them.