Firefox 3.5 consumes 100% CPU

After few minutes running Mozilla Firefox 3.5 the firefox.exe process starts to consume cca 100% of one CPU. Closing Firefox application does not help. The process firefox.exe is still there and still consuming cca 100% CPU of my Thinkpad (i.e. Task Manager presents total 50% as it’s dual core).

Anyone else having same trouble?

46 komentářů: „Firefox 3.5 consumes 100% CPU

  1. ludek 07/07/2009 / 14:11

    50% on dual core means firefox, in fact, takes 100% of one core

    To se mi líbí

  2. Milan Borůvka 08/07/2009 / 11:22

    You are right Ludek, with 50% of dualcore CPU I mean total usage (i.e. 100% of one CPU).. Sorry for not being precise 😉


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  3. Anonymous 23/07/2009 / 18:31

    i got a quadcore – same problem, if not even worse. i sometimes get firefox (3.0.11) up to 90%…
    reinstalled it – no changes
    installed 3.0.10 – still no changes

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  4. Anonymous 03/08/2009 / 03:05

    ok so its not just me firefox upgrade killed my system and my son's as well the unistall seemed to do the trick.. anyway of getting the old 3.o back??

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  5. Anonymous 04/08/2009 / 20:32

    I have the same problem with high CPU. Have hade it with all Firefox 3.x versions. Currently I'm on 3.5.1. Starting to get tired of this. I've searched the web without finding answers that helps. Do I have to stop using my favorite browser?

    To se mi líbí

  6. Anonymous 05/08/2009 / 14:50

    I have the same problem on VISTA 64bit. I may need to change my browser this time.

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  7. Anonymous 06/08/2009 / 00:16

    After upgrading to 3.5.1 I've had the 100% CPU problem as described by Milan. Tried reinstalling but no improvement. Upgrading to 3.5.2 makes no difference. Adobe Flash upgrade to doesn't help.

    At first I thought it was related to a particular type of site (e.g. streaming, animation, pop-ups) but now am convinced the problem happens irrespective of sites visited. It just seems to happen sooner with CPU-intensive sites.

    Attempting to exit from Firefox causes the browser window to close, but the CPU-burning continues, and the memory is not freed (frequently 400MB is still occupied). Using Task Manager to kill the process is the only way to stop it.

    To se mi líbí

  8. Anonymous 10/08/2009 / 06:51

    I've been watching Milan's blog, and it's quiet out there, too quiet. CPU looping in a production app is a MAJOR PROBLEM. Those few users who are, as Bill Gates likes to say, „technical,“ will know what's up, because they run performance monitors on their own systems. The 99.9% not into techie stuff will maybe notice that nothing runs well if Firefox is running, and conclude that the world's best browser has turned into a pig.

    I hope the silence out there is because those with responsibility for fixing the problem are so busy working on it that they haven't time to assuage the fears of their about-to-become-former users.

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  9. Anonymous 11/08/2009 / 01:24

    I happened across this thread while searching for an answer to this problem, and I previously read that Flash is the culprit. However, I'm using the quickjava plugin, which allows me to diable java/javascript on the fly. I also have a secondary display on my laptop which gives me realtime CPU usage. As soon as I disable Javascript, the 100% CPU utilization drop to 0%.

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  10. EJEvo 13/08/2009 / 20:26

    Frustrating this has been going on and on, and Mozilla has no answer for it, but I suspect it may be an add-on related issue. I have found if I remove all but a few „core“ add-ons, the issue goes away. But when adding them back in, there eventually comes a point where the instability returns. The kicker is it doesn't seem to be related to the same add-on as the final straw. So who do you point a finger at?

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  11. Anonymous 14/08/2009 / 23:34

    Good observation, EJEvo. Maybe you would know: is there some stack or queue in Firefox which is filled, eventually to overflowing, as more add-ons are installed? Possibly the „last straw“ add-on overwrites a table or even some code.

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  12. Anonymous 16/08/2009 / 19:15

    Same problem here.
    Interesting enough, if I try out „songbird“, it also begins to eat up CPU ressources, especially AFTER quitting the program. Same as with Firefox.
    I don't care about songbird, but Firefox is pretty unusable this way :(((.

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  13. Milan Borůvka 18/08/2009 / 05:52

    I beleive the problem is indeed connecgted with some add-ons. I disabled Java Quick Starter add on, and also Evernote Web Clipper (this is because there's still no version compatible with FF 3.1.2, I do not say that Evernote causes problem). Other add ons such as Ad Block etc. are enabled.

    And I have not experienced the problem anymore!

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  14. Anonymous 20/08/2009 / 03:03

    Problem just started on one of my computers.. out of the blue.. don't know why

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  15. Anonymous 20/08/2009 / 08:08

    Guys, I am using FF(3.0)on Laptop AMD Athlon x64, 2 Ghz, 1.5GB RAM and Vista 32bit home basic for such a long time… I did not find any issue but I am facing high CPU (high like 100%) usage after updating flash with latest patch (Version :

    Problem occurs only, when I watch online movies from any source i.e. youtube, megavideo, veoh etc… as all these sites uses flash so I thought that's the root cause…

    On the other hand…

    I have a Desktop PC Intel Xeon, 2GB RAM, XP and FF 3.5.2 with the Flash version( & n number of Add ons & plugins(Including 1st PC's)… but it is working fine with any movie site.

    Now I am confused what is the root cause?
    >Is it Add-Ons…
    >Is it JavaScript….
    >Is it Flash latest patch (…
    >Or some thing else?

    I did update my laptop with FF 3.5 but did not work.. still facing the same high CPU usage problem. Well what ever the cause is, we need to find out.. 'coz I just cant think loosing FF… & I cant stop watching movies on my laptop as well… 🙂

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  16. Anonymous 24/08/2009 / 20:46

    FF3.5 is killing my CPU usage – pegged at 100% when sitting on an idle page. Now I'm SURE mozilla knows something about this. Let's gets FIX – SOON… please?

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  17. Anonymous 30/08/2009 / 17:51

    It may be java that is the culprit. I see the same symptoms with Safari 4, IE 8, Chrome and FF3.5 on the same platform.

    Searching indicates that many believe it to be a java scripting issue, not a specific browser.

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  18. Anonymous 03/09/2009 / 19:50

    In my case, partial solution was setting javascript.options.jit.content to false in about:config. However, this just made the CPU load change from permanent 100% load into kinda „saw“ curve with peaks repeating about every three or four seconds. Then I noticed one page with strangely malformed layout – there was constantly repeating some phone number. After closing this tab, the CPU-load curve became flat at about 5%. At reopening the url there was the saw again. I also tried behaviour with javascript.options.jit.content=true and closing the tab, but the CPU load remained at 100%.
    For me, it is a combination of the about:config settings and the Skype plugin.

    To se mi líbí

  19. Anonymous 08/09/2009 / 11:46

    Same problem even after Firefox is closed -and have had it for years. Only way I can to stop is to kill the firefox process in the Task Manager.

    It only occurs sometimes. Very bad programming. This should have been fixed years ago.

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  20. Anonymous 20/09/2009 / 04:56

    Thanks, SergioMC. You are more helpful than all of Mozilla, as far as I can tell. Being able to control animations is a great relief in itself.

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  21. Anonymous 21/09/2009 / 20:04

    running xp on a 2.5 athlon machine tuned up and had no problems for ages, old firefox very good adn stable, since upgrading to 3.5 then 3.5.3 massive mem usage, had over 628,200k and 99% cpu usage while sitting on yahoo home page so not impressed, so disabled the skype, yahoo, framework and java quick start ad ons and now cpu reports around 22% and memusage back sub 100,000k 🙂

    To se mi líbí

  22. Anonymous 08/10/2009 / 16:11

    SergioMC link didn't do it for me, the issue kept surfacing. But I found a possible cause myself, including a cure for the web-app I'm building.

    I'm building a web-application myself using GWT (thus my application is heavily relying on javascript AJAX XMLHttpRequest calls). In the application I open a pushback channel. The server will timeout this channel after a set time sending an object back denoting that if the client is still running, it should re-open the channel. After opening my webapp after exactly this time-out period, the CPU load jumps to 100% on a single core.
    The re-open of the pushback channel was done in the event handler receiving the timeout message (in GWT terms: In the AsyncCallback's onSuccess() method).
    The solution is to use a DeferredCommand to re-open the pushback channel in the onSuccess() method. That way, Firefox can finish processing the receipt of the message, before re-opening an asynchronous call to the server, without getting confused.

    I bet the underlying javascript AJAX XMLHttpRequest is used on many web-pages nowadays, and that many applications misbehave (or Firefox should be fixed to handle this)

    Cheers, Aart

    To se mi líbí

  23. Anonymous 18/11/2009 / 23:07

    Firefox you suck!After swapping back to FF now that it supports digital persona i find this maxed out CPU when viewing FLV problem.No problems at all with IE7 other than i dislike IE7.I have been waiting patiently for the compatability issue with persona to be fixed as i really dig the fingerprint reader on my new HDX16T and FF has been so much better than IE….not anymore FF you suck…and after seeing how long this problem has gone unaddressed i am kicking you to the kerb.

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  24. Anonymous 07/12/2009 / 15:04

    IE8, Safari, FF and Chrome all exhibit the identical behavior.

    Does anyone know if Sun has even acknowledged their role in this issue?

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  25. Anonymous 05/03/2010 / 15:34

    Hi. I don't know if it helps but (as i read above), I DISABLE THE PLUGIN „MICROSOFT.NET FRAMEWORK ASSISTANT 1.1“ (which installed by itself) and every back to normal, now my firefox loads faster and closes ok, post if it helps.

    To se mi líbí

  26. Anonymous 06/03/2010 / 10:49

    It seems everybody who's using FF is having the same issue as mine even though I have disabled every Plugin that I had and it still hogs up my CPU and memory resources. I'm using the 3.5.8 version and they say that 3.6 is better and faster than the 3.5's but it doesn't say if it uses a lot of CPU resources or Memory… Is the 3.6 the fix of all the lower versions of FF?

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  27. Anonymous 15/03/2010 / 21:30

    I have 3.6 and having the same issues here. Got a quad core and they all read 100% and stay that way for about a minute after closing Firefox.

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  28. Anonymous 23/03/2010 / 00:45

    Got this problem to, im going to switch back to IE7 because of this…

    to bad firefox was such a good browser, now its like like a pig, eating all resources ect..

    if they solve it, i will be back, but not sooner then that, that's for sure.

    To se mi líbí

  29. Anonymous 30/03/2010 / 01:16

    I am having this problem as well. It hasn't been too bad lately, but now it is running the remaining CPU resources that aren't used by other processes. Once I close the FF window, the CPU settles down and my fans shut down shortly after. I tried shutting down completely and rebooting and then loading my AOL and then FF and it is now going to this 100% remaining CPU consumption right off the bat. I previously thought that FireFox was a good solution to the issues I was having with MS IE but now I think I'm gonna have to give the IE a try since FF makes my internet interactions unbearable and slow and I'm just hoping my fans can keep the CPU cool enough for me to post this comment before my notebook catches fire. All three fans are running 100% to keep my system cool.

    Where is FF anyway? Don't they read this issues the users are having? I'm not impressed with the length of this discussion and the number of users having issues with it and no comments from FF? Hummm…. I think it was a good thing that has gone bad and not sure much is being done about it. Too bad. I really liked using FF better than MS IE, but… Here I go back… Please force an update when the new fix is out so that if I run FF again, it will give me an update notice.

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  30. Anonymous 30/03/2010 / 11:55

    Firefox CPU problems here as well, running Vista with FF 3.6.2, no problems with other browsers but FF takes 60-70% for example when I make a hotel search at

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  31. Anonymous 04/04/2010 / 12:54

    Addon solved the Problem for me, too.

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  32. Anonymous 07/04/2010 / 13:39

    This problem seems to be very prevalent at the moment and the Mozilla people just seem to be ignoring it. It is either a bug in Firefox or a bug in an add-in. There should be defensive code in Firefox to stop add-ins from running CPU-hot.
    Sometime if I continue to suffer for long enough, I get unresponsive script warnings „A script on this page may be busy, or it may have stopped responding. You can stop the script now, or you can continue to see if the script will complete.“
    Today's example script (the script is not often the same) is chrome://mozapps/content/extensions.xml:0
    Please can someone try to sort this out, before we are all forced back to IE.

    To se mi líbí

  33. Steve1025 24/04/2010 / 22:35

    I recently upgraded FF on my VISA to 2.6.3 and ran into the heavy cpu usage problem. I disabled „MICROSOFT.NET FRAMEWORK ASSISTANT 1.1“ and my system too went back to normal, and my internet access response time went from 2.6 to 9.9 The cpu still bounces around a little but not as bad as it was.

    To se mi líbí

  34. Anonymous 30/04/2010 / 06:37

    Had the same problem with firefox 3.6.3, and solved it by disabling java quick starter.

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  35. Anonymous 11/05/2010 / 20:45

    What i am reading is if you disable everything, it works. cool. IE here i come…

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