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Firefox 21.0 on OS X 10.8.4 still has a memory leak that occurs with no Add ons, 1 tab and leads to 3GB of memory usage in 10 minutes.

  • 36 replies
  • 40 have this problem
  • Last reply by John99

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While using Firefox 21.0 on OS X 10.8.4 with 4GB RAM, Firefox memory usage marches up and up until at 3GB (on my iMac) Firefox hangs and is 100% non-responsive and must be killed with Force Quit. It takes 10 minutes to occur.

No Add Ons One tab

All Replies (20)

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Thank you for the update! I just installed it and I will test.

Thank you!

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x-link /questions/956369#answer-448676
Info in thread How do I stop a firefox.exe memory leak?

I suspect it is unlikely a long standing problem will resolve on upgrade to fx22.

  • The overly simplistic next suggestion would be to recommend FirefoxReset.


  1. You may wish to post your troubleshooting info into the thread as it was not included in the Original Post. Possibly Tyler may find it useful.
    • use about:support
  2. As an advanced user, and for testing purposes you may also wish to give consideration to installing an new additional version of Firefox in a clean profile. Let's go the whole hog and try with Nightly in anticipation that you will find something where a bug will be filed

P.S. with 16 years C++ experience you may yourself be interested in the developers info

Modified by John99

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  Unfortunately, the problem was WORSE in FF 22.0. I regressed to FF21.0 and shut off automatic updates. I may even go back to FF3.6, which is the last one where I didn't see this problem.
  Thank you for trying but as a longstanding developer I know that pervasive memory leaks is a sign of a broken development process. Thank you for trying...
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Firefox 21 is no longer secure, so please update back to Firefox 22, then try a Firefox Reset. Memory leaks are an over used term, and likely not exactly what you are seeing, so there are lots of troubleshooting methods we should try here before you throw in the towel. And I'd rather you use another browser than old versions of Firefox.

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Tyler, Don't worry, I use Firefox as little as possible because of this problem. And I did try updating to 22.0 with a Firefox reset. The problem was worse.

I will also add that I think the problem is related to the application cache. The application cache always showed 0 bytes but when I clicked on it and the regular cache clear several times, I saw the memory held by Firefox drop. So, the 0 bytes held by application cache is obviously not reflecting the actual value held.

Finally, if you read my comments above, I have been a professional software engineer for 16 years. What I am seeing--the steady march upwards of RAM consumption, looks just like a memory leak.

Please look at the app cache.

Modified by curmudgeon99

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Have you even tried any of the troubleshooting steps? The fact of the matter is that Firefox 21 is much better at handling memory usage than any versions of Firefox before (look at any benchmark or test), so this is an issue on your computer alone, and thus, not a memory leak or issue we can solve in Firefox itself. This support site however can help you solve this issue, but you aren't being responsive to the suggested troubleshooting steps.

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Let's review the issue so far.

My iMac is running the latest version of the OS. My instance of Firefox contains zero add ons. I was running one tab. The memory usage began at around 200MB and marched upwards with little change until at around 2.93GB, Firefox stops responding,

I have seen this with a brand new profile. In fact, I restart my machine when this happens. No other application that I run including IntelliJ or MyEclipse ever causes this problem to happen. Only Firefox.

I understand that Firefox 21 may have been an improvement but I have been seeing this problem in Firefox 21. Firefox 22 showed the problem even worse.

I will get the troubleshooting information and post it. But I'm of a mind to just uninstall Firefox.

In my career, whenever a developer starts down the road of arguing against a bug's existence--blaming QA--the developer is heading for a large helping of crow down the road. I have never seen an observed defect that ended up being phantom.

Thank you for your time. There is no more important feature in any application than stability.

Modified by curmudgeon99

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First, I'm not, and 99% of the people answering questions on this forum, are not developers. This isn't a bug reporting database (we have bugzilla for that) this is an end-user support site. So, if you want to file a bug, go to mozilla's bugzilla. If you want help solving an issue in Firefox, we can help you here.

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No one is denying you have a problem. Unusual severe in fact getting to 3GB in10 minutes. I am not sure I have ever got that high, although trying with a few hundred tabs I have got over 2GB with Firefox remaining functional.

Others ARE sure to have a similar problem
but it almost certainly will be exceedingly rare. I could hazard a couple of guesses at the probable reason but I will leave it to Tyler to work on that.

Looking on the bright side you have

  • an easily producible problem
  • that is massively noticeable within a few minutes.

It should be an easier problem than many to troubleshoot.

Good luck with your problem. Hopefully it will be resolved, and you will get a working Firefox back without risking using legacy versions.


For some reason I do not think the aggregated Telemetry results are published. I am guessing that sort of data will be exposed in FHR eventually. Regardless of number of apps or tabs how common is >3GB usage on a Firefox22 desktop?

I would not be surprised if that occurs less than 2% of the time.

I note system-requirements are only for 1/2GB and of course on Windows Firefox is only a 32bit browser ordinarily.

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John, I'm not sure if telemetry gives us memory usage (and the data from any of our data sources are very locked down for privacy issues). Memory usage is a tricky thing and we can't set an arbitrary number that says "Anything over 1GB is high) or something like that, as there are many many variables (plugins, History and cache size, open tabs, even the amount of downloads you have in your download list can all have an impact on your memory size, though some are smaller than others).

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Aggregated telemetry info now public at

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I am having the same issues of memory leaks with FF22 in windows. Although I do have a fork of Firefox: Palemoon which works just fine.

No leaks at all. I would give that a try it's much more stable than regular FF...

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Not useful to me. I'm using OS X

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I released that after posting but did find these:

If you search the Addons area for 'memory' there are 3 addons that I think may help (I installed them). They seems somehow to be helping keep it below 1500mb for my 100 odd tabs :)

Memory Fox

Memory Restart


Modified by joshcloud9

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If those add ons are available for the FF on Mac, I'll give it a try.

Still, this is no substitute for Mozilla fixing the underlying memory leak problems.

Thank you.

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Hi curmudgeon99, what page are you viewing when observing the increasing memory consumption? Do you notice Firefox refreshing any content on the page or refreshing the page itself?

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I have described it above. I am monitoring the memory consumption through the OS X Activity Monitor. The increase in memory happens when going to any internet page that has multiple links. Click on one link, view the results, click the back button, click the next link, view the page, go back, Under that scenario, memory consumption steadily climbs unless I actively clear the App cache, though Firefox itself reports that the App Cache is using "0 bytes". So, the App Cache is not correctly reporting the memory it is consuming.

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Hi curmudgeon99, I thought you were just sitting there with one tab open and memory usage increased by itself...

Every time you load a page Firefox is caching resources on these pages, and some of that is in memory. I don't know how quickly you are leaving the pages, but Firefox may fail to release memory if some resources do not load to completion (this has been observed in some "slide show" type scripts with image loads).

What is the "App Cache" you are clearing -- is that Firefox's offline storage feature? You're saying that in the dialog it shows 0 bytes but if you clear it then memory usage goes down?

Modified by jscher2000

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Hey curmudgeon99, I have one of the Firefox memory devs interested in your problem.

He'd like you to visit about:memory as soon as you open Firefox and before you begin any browsing. Then, copy and paste everything on the page to and return to this site and give us the url to the pastebin.

Then grab another copy of the about:memory data during the halfway point of 10 minutes.

And lastly, get one more copy of the about:memory data before Firefox becomes unresponsive but is near the 2GB high memory you speak of.

So you should have about 3 pastebins worth of about:memory data when you're done and I will show that to the memory dev and report back on his findings.

It'd be nice if you could just paste that data here but the first part of it becomes mangled & unreadable due to how the "Main Process" data section is formatted. See my example attempt here:

  1. 1
  2. 2