Firefox Consumes the CPU

Category: Quickies


No matter what I do, including extensive research on Firefox site and the Internet, I still get CPU usage of 99% with Firefox, and it won't go away. It stops my system until I shut it down with ctl-alt-delete. Sometimes, it shows 0% usage and then won't even load. I'm pretty good with this stuff, and this still stumps me. (XP2 1G RAM, all up to date, trust me...)


And people wonder why I'm sticking with Internet Explorer. :-) Anyone else have this problem, or a solution?

If you think you know the answer, post your comments below.

This article was posted by on 31 Aug 2005

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Most recent comments on "Firefox Consumes the CPU"

(See all 42 comments for this article.)

Posted by:

James R. Hall
17 Sep 2007

Bottom line up front: use NoScript. I must say that this problem doesn't come up that often for me, but it's a pain when it does.

The hassle with NoScript is that you have to allow for scripts to be run for each site. A pain in the beginning, but less so as time goes by (sort of like Zone Alarm firewall).

Posted by:

Saurabh Sen
22 Oct 2007

I support James R.Hall. Use NoScript and the problems do not appear. Had the same problem with Firefox even with latest versions which has now gone using NoScript.

EDITOR'S NOTE: No argument there... if you disable the function that contains the flaw, you won't be affected by it.

Posted by:

13 Nov 2007

I suspect these cpu and memory problems of Firefox and other browsers and programs are not due to any one problem but to a confluence of several problems, and I could elaborate on each of the issues... but they all have one thing in common: Windows. Are any of the above complaints from anyone running Linux or BSD Unix? I think not. The problem is with the shoddy way Windows is implemented: they rolled their own tasking (non-preemptive) and virtual memory, and they were amateurs suffering from NIH syndrome (Not Invented Here syndrome) - they insist on doing things their own crappy way, ignoring decades of operating system research and experience. The result is a staggeringly bad operating system which most of us are unfortunately dependent on. And it's known to have memory leakage issues. And horrendous security issues (when the Chinese military broke into the DOD network and accessed the email of the Secretary of Defense recently, I'll bet you dollars to donuts the SecDef was running Windows).

And please, don't give me any crap about the superiority of Macs. I've done development on Apples and Macs pre-BSD, and it was just as crappy, just done differently.

And I'm not giving solid gold marks to the Linux and Unix weenies either. Part of the problem (I suspect) with Firefox and Thunderbird and their ilk is that their developers develop them on Linux/Unix platforms and are _extremely_ sloppy with their tasking and memory usage. Which you can get away with on Linux/Unix because the tasking (pre-emptive) and virtual memory are implemented correctly, unlike Windows, and cover up sins of programming sloth. On Windows however, the result is, when sloppy programming meets crappy operating system you get periodic and random catastrophes. Which is what we're seeing with Firefox.

Either Mozilla has to tune its crap better for Windows, or Windows has to improve. I ain't placin' any bets either way.

Now if only Linux (any version, please, Ubuntu, PCLinux, Knoppix, any of them, please) would just become as usable a platform as Windows, we could all get off Windows and start getting some real work done.

EDITOR'S NOTE: Interesting, but I just read an article today titled: "Fix Firefox's memory problems, says Mozilla director"


Posted by:

19 Nov 2007

I am having the CPU drag and slow-motion browsing experience whenever I bring up certain websites with videos (like youtube) and foreign language fonts (

I am having this problem across different browers (IE, Firefox and Opera). My machine is XP Pro SP2 with 2 GIG ram. It's such a crapy "internet" experience just around the time people are talking about IP TV :) My next door neighbour just bought a new laptop having no luck with this issue on her old laptop.

EDITOR'S NOTE: It's perhaps a function of your Internet service provider. Does trying at a different time of day help? If not, consider upgrading your video card.

Posted by:

alan johnston
17 Jan 2008

Firefox 2 has started to do this on my PC now. Firefox v2.0.0.11. Windows XP Pro SP2. All I have to do is fire up Firefox 2 with a blank startup page, then wait a few minutes. Suddenly the Firefox.exe goes from 0 to 99% CPU and stays there. If I close Firefox, the window closes but the process remains in task manager - have to kill the process. Happens with Firefox in safe mode with no addons as well. Mystified.

Posted by:

alan johnston
18 Jan 2008

Have found solution to my problem. Might work for other Firefox 2 users. In tools > options > security. Untick the 'tell me if the site i am visiting is a suspected forgery'. box. CPU use went from 99% to 0% once I had done this (had to restart firefox first though). This article might be usefull

Posted by:

01 Feb 2008

I have Windows XP Home SP2 and Firefox version I have had this problem with Firefox as well. Every once in a while, Firefox will spontaneously jump to 99% CPU. However, it gets a bit tricky after this. After I end firefox.exe from the Task Manager (b/c clicking the close button won't work) my CPU goes back to idle. But when I click on any other window, THAT application suddenly jumps to 99%. If I end that one, the same thing happens with the next application/window I click. This keeps cascading until my system locks up, and I have to do a hard shut-down.

If I then re-boot and log back in, my computer hangs while it is logging in, and I have to hard shut-down again. The only way I've to restore functionality is to boot in safe mode and use System Restore to the latest point before the incident. After that, everything works fine. This whole process has happened to me three times since upgrading to Firefox 2. Anyone have any ideas?

Posted by:

12 Feb 2008

Thank you Alan, your solution worked for me also

Posted by:

06 Aug 2008

I had the same problem. Quite a lot of plugin in firefox, not few tabs open. I am browsing in Chinese website with a lot of ad and heavy (not to mention useless) content. Result : CPU 95% just for Firefox. I tried the plugin NOSCRIPT and Firefox jumped back to a reasonnable 0%. Thank you NoScript!!

Posted by:

29 Sep 2008

Thanks Alan, that seems to have done the trick! What a weird thing for FF to do!?

Posted by:

19 Oct 2008

Some users that have an ATI Radeon Card are experiencing this (me as well) with the latest ATI drivers. To remedy this problem download the ATI Radeon OMEGA drivers based on 7.10 (NOT 7.12 AS YOU WILL HAVE THE SAME PROBLEM).

This helped me tremendously and now FF2 and FF3 run fine and speedy with hardly any cpu/ram usage.

Posted by:

06 Nov 2008


I am having Sony Vaio laptop (1.6 GHz, 80 GB hard disk and 1 GB RAM). Since 3 months, I am facing major issues. Whenever I start browing (IE or Opera or Firefox) or even when connect external hard disk (to copy data to my laptop), CPU shoots to 100% and stays there making my machine dead slow. Finally I did the following:

1) Did the complete system restore and now laptop is set to factory setting

with no extra software and all 80 GB free. So it is as good as new system

2) also increaded RAM to 1 GB from initial 512 MB

3) have done all performance related task like Defragmentation, Disk Cleanup. I guess since its a fresh system recovery, so no need of doing this.

4) Have Mcafee running on my machine and no virus threat detected.

5) All drivers are up to date

Finally I found something related to my issue on microft support site.

This was the exact problem what I was facing and I upgraded my windows XP Professional SP2 to latest SP3 patch. STILL THE SAME OLD PROBLEM PERSITS.

Any solution would be really be appreciated.

Posted by:

21 Jan 2009

Thanks Alan - I did what you suggested and it seems to work so far - I have FF V3.0.5 -- Andy :-)

options > security. Untick the 'tell me if the site i am visiting is a suspected forgery'. box.>>>>

Posted by:

30 Apr 2009

- I - today got this problem - I did system restore - and it went away. If you didn't do that on time - sorry - Firefox is a great browser.

P.S. Last thing I did was install Adobe Shockwave Player - I bet that patched me...

Posted by:

30 Apr 2009

- I've just now unchecked the dodgy site warning - and it's even lower (CPU) and stable - thanx.
- And remember - anything wrong - do system restore straight away.

Posted by:

12 May 2009

Thanks Alan,

I don't understand why this trick works, but thanks a bunch. I was about to transition everything to internet explorer (which I don't like).

Cheers to you!

Posted by:

19 May 2009

Look at, especially the part about deleting the cookies.txt and/or cookies.sqllite. This helped for me.

Posted by:

11 Oct 2009

Get more ram.

Posted by:

24 Mar 2010

Try this to fix the Firefox CPU usage problem.
enter in address bar about:config
find entry browser.catch.memory.enable
double click to change value from true to false.
restart the browser.
This worked for me.

Posted by:

06 Apr 2010

try this.
they helped me with high CPU and freezing in Firefox
.. windows xp.
also, disabled indexing, takes a lot CPU
and auslogics disk defrag. amazed how quick and efficient it is.
good luck

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