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How to Determine which Firefox Add-ons are Using the Most Memory

I use Mozilla Firefox 3.6 all day, opening and closing tabs quite regularly. I am noticing over time that the firefox.exe process size keeps growing and growing over time.

Initially I put this down to memory fragmentation caused by opening and closing tabs, but now I am suspecting that there is a memory leak in one of the add-ons that I have installed.

The problem I am seeing is that when the process size gets to about 1.5GB in the "Mem Usage" stat in Task Manager (and it gets there quite regularly), Firefox freezes up.

These are the add-ons I currently have installed:

  • Adblock Plus (1.1.3)
  • English (Australian) dictionary (2.1.1)
  • Gmail Notifier (
  • Google Reader Watcher (
  • Java Console (6.0.11)
  • Java Console (6.0.07) (Not sure why I have 2 versions of this)
  • Java Quick Starter (1.0)
  • Session Manager (

Are there any known memory leak issues with any of these?

Could something else by causing this problem?

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marked as duplicate by Arjan, Ivo Flipse Mar 22 '10 at 9:37

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

I feel this is a duplicate of the more generic "How to Determine which Firefox Add-ons are Using the Most Memory" at… – Arjan Mar 21 '10 at 23:03

I had similar symptoms, so I started disabling addons at random. Eventually, the bloating stopped (I believe it was After The Deadline, but I could be wrong.)

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Thanks for your answer - I don't have that add-on, but I have updated my question with the add-ons (and versions) I have installed. Do you know if there are any issues with any of those? – LeopardSkinPillBoxHat Mar 21 '10 at 22:03
@Leopard; None of them jump out at me, so I suggest disabling them one by one until you find the culprit(s). – Phoshi Mar 21 '10 at 23:10

I think the main problem with apps like firefox that have constantly changing memory contents (due to opening and closing pages, changes to the DOM while these pages are open, other scripted activity in the pages, activity by plug-ins and so on) is memory fragmentation within the app's memory management routines as well as more explicit leaks.

I notice this quick often (though less often with FF3.5/3.6 than earlier versions), so have one of the many simple quick-restart add-ons installed. Firefox's session manager does a good job of reopening all my windows and tabs if I have any active at the time. Session level cookies seem to be preserved too, so I stay logged into applications like Zimbra and Pivotal Tracker.

I've never had the issue lock Firefox up as you describe, though it does get to the point of things slowing down so it may sometimes pause a couple of seconds when opening new tabs or closing old ones. I think this growing delay is due to it needing to work harder to maintain the growing and increasingly fragmented memory allocation structures. After the quick-restart this problem (and the excess memory used) is resolved for a while (until the memory allocated grows again, at which point I restart again).

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Thanks David - I have been restarting as a solution to this problem, but it feels like a workaround more than a solution. I guess one answer is to use Chrome which creates a separate process for each tab :-) – LeopardSkinPillBoxHat Mar 21 '10 at 22:47

If this were Stackoverflow, I might point you to the Debugging memory leaks page at the Mozilla developer wiki. I suspect you don't want to go to that much trouble though.

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@Hugh - Actually, I'm a software developer so I may be able to give that a go. Thanks :-) – LeopardSkinPillBoxHat Mar 22 '10 at 3:11

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