I work as a web developer and for that I'm using Firefox with Firebug. Recently, I have noticed that after two hours of work, the firefox.exe process needed more than 1 GB of my working memory!

Even if I close the window, the process still remains in Task Manager and the only thing I can do is to 'kill' the process.

Any suggestions?

I'm using Windows 7 with 2 GB RAM, Firefox 3.6.8 in which I normally have opened 10 tabs.

migrated from stackoverflow.com Sep 2 '10 at 8:34

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  • 3
    If you reuse tabs intensively, it might have to do with that since Firefox keeps lots of history per tab then. Or perhaps an extension is leaking memory or something like that. – Rob Sep 2 '10 at 8:34
  • I'm having the same problem and I just offered a 50-point bounty on this question. I don't use Firebug at this time, so that's not the issue. I disabled all my other plug-ins. I don't even use this machine (where I have the problem all the time) for development - it's literally just for browsing the web! – Alex R Feb 7 '11 at 5:57
  • You should have started a new post, as your bounty doesn't seem to fit the question except in title. – harrymc Feb 7 '11 at 11:41
  • I believe Rob is correct. I've noticed the same behavior with multiple tabs or with leaving tabs open over time. – 에이바 Feb 7 '11 at 19:35
  • Have you set the maximum RAM and disk cache usage limits as I have defined in my answer? – Breakthrough Feb 11 '11 at 17:30

It sounds like two separate problems. First, Firefox is known to be a memory hog. There are ways to keep this to a minimum, including getting rid of addons you don't need, as well as this:

In about:config, add a new Boolean value named config.trim_on_minimize, then set it to True. I'm still evaluating this tweak myself and can't yet say for sure whether it helps.

Second, if the Firefox process doesn't stop when you close its window, try waiting for a while. I find that once Firefox is using a ton of memory, it can take some time (up to 30 seconds or so) for it to close down completely.

  • This doesn't actually limit the amount of RAM that Firefox uses though... :S – cp2141 Feb 11 '11 at 18:34
  • 1
    trim would just clean up, yes? – Sam Feb 12 '11 at 7:37
  • @Sam yes, that is all trim does - clean up. See my answer for how to set hard RAM limits. – Breakthrough Apr 14 '11 at 21:54

I am unsure whether or not newer versions of Firefox have this option enabled by default, but there does exist the option to provide maximum RAM and disk cache usages in Firefox. This is much different than changing the memory cleanup and garbage collection options, as you can force Firefox to use less RAM and use more disk cache.

To limit the amount of RAM Firefox uses before using the disk cache, navigate your browser to about:config. In the Filter, enter "memory", and you should see:


If you don't, then you will need to manually create this key as an integer value. This integer value represents the memory cache (in kilobytes) that Firefox can use. I personally set this value to 131072 (128 MB). To avoid Firefox running out of memory, you can then increase the disk cache it uses by changing the following variable (you can just use "disk" as the search filter).


Again, this is the disk cache (in kilobytes) as an integer value, and if it does not exist, you must create it. I personally set mine to 307200 (300 MB). Note that this is different from the amount of storage Firefox uses to store offline files or your history.


Firefox is known for being very resource heavy after long periods of use, you could try uninstalling unused addons to see if that has any effect.

  • Yes, Firefox is very hard on system resources. If your system gets bogged down by it you may have to upgrade systems or switch to another browser that does better on limited resources. – Brian Knoblauch Sep 2 '10 at 17:06
  • An upgrade for a browser would be insane. It is my one major beef with firefox that it is just so damned heavy! – Toby Oct 1 '10 at 14:48
  • Why should anybody use Firefox if it uses more memory than IE? It seems a bit pointless. – Alex R Feb 7 '11 at 5:55
  • @Alex - Because it is a standards based browser that doesn't break the web. – Toby Feb 8 '11 at 9:41
  • Because of the plugins! – Sam Feb 12 '11 at 7:31

You could try AFOM which

memory recovers Memory Leakage within a running instance of the Firefox browser application.

I'd also recommend that you vacuum you databases regularly. Ccleaner now has this functionality.

Alternatively, a fresh installation might work. It can also help to troubleshoot the issue. If you bring back the extensions one at a time you might see if one of them is causing the problem. After uninstalling, be sure to remove all traces of your profile. Revo uninstaller should do this thoroughly.

  • The AFOM link is (effectively) broken now ("Search Results for "afom". No results found."). – Peter Mortensen May 23 '12 at 16:40

This seems like a known Firebug issue : Firebug memory leak - over 600MiB seen used.
This problem report was opened in 2007 and is still open ...

Another such open issue is When Firebug is enabled, Firefox uses huge amounts of memory and CPU.

Firebug is therefore listed in the Problematic extensions list of Mozilla.

You might have a look at the Firebug Memory Profiler, although it is said to be in a real alpha phase, which might give a hint regarding the problem.

Otherwise, your only solution is either to live with the problem by restarting Firefox or getting more RAM, hammer on it in the Firebug Community, wait for a fix (may take years), become a Firebug developer and fix the bug yourself, or use another debugging tool.


Which version of Firefox are you running? This is not typical behavior. Maybe enabling Firebug only for the sites you're working on will help.

  • 6
    Unfortunately it really is typical behaviour. – Toby Oct 1 '10 at 14:48
  • 1
    Firebug is not the problem. I don't use Firebug and I just found this thread because I googled "Firefox 1gb". – Alex R Feb 7 '11 at 5:55

It doesn't matter how much memory Firefox is using. The operating system manages it better than we could, so don't think about it. Being slow is another matter, which is clearly Firefox's habit.

You might (and should try to) be able to use Chrome and find extensions there. Even Opera's Dragonfly is better than Firebug (so I hear, I have never used Firebug myself).

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