After using Firefox for several days without restarting, my memory usage is extremely high. I have around 40-50 tabs open. Just now my memory usage was over 4gb and Firefox was extremely slow. After restarting and restoring all my tabs memory usage was only 700mb. I went and visited each tab individually to make sure they were all loaded and it climbed to about 2gb. This is a lot but not too unexpected for this many tabs open. I'm not sure how this doubles while keeping the same tabs open, though.

Is this expected, or the result of a memory leak of some kind? Is there anything I can do to free up additional memory? The "minimize memory usage" button in about:memory doesn't do much. I notice a lot of the memory is taken up by javascript. I'm running version 29.0, no add-ons other than firebug.

  • 1
    I was about to suggest that you disable firebug, even before I read that this was the only add-on you have. Firebug was unambiguously the cause of the memory usage when I did my development in Firefox. Now I use Chrome, so I can't say if this is still true. Feb 12 '14 at 21:42
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    Most of the firebug functionality is replicated in the build in FireFox Web Dev Tools anyway. Also update to the latest version of FF of course.
    – Dom
    Feb 12 '14 at 22:00
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    Latest stable version is 27.0, right now. You should specify the operating system you're using. Also, try disabling Firebug to see whether it makes any difference.
    – and31415
    Feb 12 '14 at 22:01
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    open about:memory in Firefox, copy the output to pastebin and post a link here. Feb 13 '14 at 7:58

Firefox has always had ongoing issues with memory leaks. While certain addons make the issue worse, even an up-to-date vanilla install can still have issues. If you don't mind third-party software as a solution, you may want to consider using a program called Firemin. Firemin is an external program that uses CPU resources to actively monitor Firefox's memory usage, ensuring it is as low as possible. The program is configurable, so you can specify how zealous you want the memory management to be.


I was seeing a huge leak too, but I don't keep 40-50 tabs open..maybe 10 at the most.

I found today that removing all the thumbnail images of sites I visited has greatly reduced the amount of memory Firefox is using (when viewed using Task Manager). (i.e. - hitting the "+" box to open a new tab and see thumbnails of sites).

Before this, I booted up my Win 7 64-bit machine wth 4 Gb Ram and after maybe an hour, my memory usage (according to TaskManager) was around 800,000K. After deleting everything, memory has been steady at 273,000 K.

Turning off and/or disabling Add-ons made no difference in my testing, though I disabled one for Lync. (doubt it made a difference).

Win 7 64-bit Pro sp1 Running FF 27.0.1.

Not proclaiming this as a solution as of yet, but so far my machine hasn't come to a crawl. (about 3 hours in so far)


Update 24 hours later: FF is still running well after I cleared all the thumbnails out.


It's the nature of Firefox to leak memory as it uses a single process to store all the tabs, and each tab of a modern webpage can consume a lot of RAM.

Untangling what memory can be released when the tab is closed is just too difficult for browser makers. Other browsers like Chrome and IE worked around this problem by creating a new process for each tab, and killing that process when you close the tab, which solves the memory leak issue, but it does mean that those browsers can become extremely slow to start when you have 10s of tabs open as the browsers must fork tens of processes.

About the only practical way to deal with the memory issue in Firefox is to make sure it's setup to reload tabs on restart and to accept that one every day or 2 it will crash.

I've ended up working around this by installing an extension to make it easy to restart Firefox and restarting it each morning.

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    Well, no. That’s not really the issue. Firefox does not leak. Extensions do. Also, process separation is mainly to improve stability.
    – Daniel B
    Dec 10 '14 at 20:57

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