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Is there anything in the current Firefox similar to the Task Manager in Google Chrome? (Shift + Esc)

There is something that occasionally takes up enough CPU to make Firefox unresponsive - but with multiple windows, each with a dozen or so tabs open, trial & error is going to take a while.

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12 Answers 12

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Resource usage can be monitored with Process Manager (the about:processes page). It has a shortcut Shift+Esc.

Process Manager


Task Manager (the about:performance page) was removed in Firefox 116.

Task Manager

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    That's nice. However, I have a 100% CPU "Web Content" process which doesn't show up here. Jul 6, 2019 at 10:43
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    Perhaps about:processes may show a process (group of tabs) which doesn't show up in about:performance Jan 20, 2021 at 17:17
  • about:processes actually showed me less information about why my computer was spinning its wheels where performance actually showed me what it was
    – EkriirkE
    Sep 20, 2022 at 7:05
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about:memory shows Firefox's memory usage details. There's also a button on that page that allows you to minimize memory usage.

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    Obviously it's not the same as CPU usage, but in my experience they're very often correlated. After killing the biggest memory-hogging tab, CPU usage & lagginess often drop noticeably.
    – peterflynn
    Aug 22, 2013 at 4:16
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    Obviously it’s not the same as CPU usage, but in my experience they're very often correlated. @ytpete, then you frequent a narrow subset of webpages because there is absolutely no reason that they would necessarily be linked. It’s simple enough to have a 1KB webpage that has JavaScript with an infinite loop and thus 100% CPU load and another with 100MB of images that uses no CPU.
    – Synetech
    Nov 15, 2013 at 3:24
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    about:memory shows Firefox's memory usage details. There's also a button on that page that allows you to minimize memory usage. Does that page have CPU load information? If not, then what does this have to do with the question asked? This “answer” should be a comment, not an answer.
    – Synetech
    Nov 15, 2013 at 3:25
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    @Synetech It's been many years since a simple JS infinite loop would do much: Firefox and most other browsers put up an "unresponsive script" message after a few seconds of that, and then the loop gets cut off.
    – peterflynn
    Nov 15, 2013 at 7:46
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    This worked great for me. While it's true that a small Javascript loop can hit the CPU without using memory, that's not what what most webpage scripts are doing -- they are making remote calls, updating and manipulating the DOM, getting invoked by plugins (like Flash), etc. All these things can result in increased memory usage (especially if the page is slowly leaking objects). I found the culprit tab, closed it, used the Minimize Memory button, and Firefox was running smooth. Thanks again!
    – Nick
    May 9, 2014 at 17:02
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The first likely culprit is Flash. Kill Flash - now.

Then it may be rogue Javascript code. Firefox's Javascript Deobfuscator extention lets you watch the count of Javascript function calls :

It is not a measure of CPU usage, but a close enough proxy : find the function with a runwaway number of calls and you will likely have caught the culprit.

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    I don't have Flash installed and I have NoScript installed. This still happens on OSX even though I have two CPUs with 8 cores and 32 GB of RAM Aug 17, 2015 at 6:46
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Firefox 16 should introduce proper built-in profiler at last.

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By using Flashblock and Nevercrash, now replaced with FlashStopper and UnloadTab you go a long way into blocking Flash or tabs, preventing CPU waste instead of tracking it. This holds, but less, for memory too. Flash, e.g. Youtube is prevented to start until you click on them, so you may launch them in several tabs and they wait for you to open the tabs. Tabs are uloaded from memory and idle until you reopen them and they are refreshed from the cache (if still available).
Shutting down the Internet for a while also works during the time you don't need it ;-)
Firefox fragments virtual memory so much that it's using an excessive amount of real memory (there is too much unused virtual memory in real memory). One needs to periodically stop and restart Firefox with the same pages. That will defragment its memory and the whole system will run faster by reducing the swapping.
On my Ubuntu system, real memory usage slowly climbs up to 98%. Then it's time to stop Firefox and restart it: it will then use less than 1MB of real memory instead of 3MB. The same holds for Thunderbird..

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  • You might also have some success using the memory cleanup buttons in about:memory. I don't know if they will work as well as restarting Firefox. I would love to see some research on that. Jun 30, 2015 at 13:24
  • Thanks. Did before, did it again, and real memory usage stays at 92% when clicking any. <br/> Regarding Flashblock and Nevercrash than I mentioned, they became incompatible with Firefox 34. A "did you upgrade to the latest version?" eternal problem. The wave is now Flashstopper and UnloadTab. Rather compatible but UnloadTab now unsurprisingly unloads tabs, needs no explicit "unloading of tabs" (fine) and "reloading tabs" acts as a page refresh (less fine, but using cache). One can set "Keep Address Loaded" when that reloading is breaking a page state you want to keep.
    – Papou
    Jul 1, 2015 at 15:34
  • Thanks for testing. :) <plug> I use my own Hibernate Idle Tabs userscript with Greasemonkey. It navigates to a light holding page after the tab has been unused for some hours. Hibernation can be forced with its bookmarklet. Jul 2, 2015 at 9:31
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Except for already mentioned about:performance, there is a Task Manager addon that meant to be a clone of Chrome's Task manger.

enter image description here

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    Unfortunately not yet compatible with Firefox 57.0+
    – Ed Randall
    Nov 17, 2017 at 7:55
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The following answer to another question may help you. The answer is written by the user "accolade".

XUL Profiler is an awesome extension that can point out extensions and client side JS gone bananas CPU-wise. It does not work on a per-tab basis, but per-script (or so). You can normally relate those .js scripts to your tabs or extensions by hand.

It is also worth mentioning that Google Chrome has built-in a really good task manager that gives memory and CPU usage per tab, extension and plugin.

Let me add some more info to accolade's answer. As of January 2012, the latest version of XUL Profiler is 1.0.4, released December 2008. It's only certified compatible with Firefox 2.0 - 3.6.*. So it clearly needs a new maintainer.

I wonder if there's any way to force the extension to work on newer Firefox versions.

Also, I wonder if it works well to downgrade Firefox temporarily in order to use XUL Profiler with your existing tabs on a certified-compatible Firefox version.

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Here around 20% cpu was not accounted for by about:performance .

Turning off "Enable add-on debugging" checkbox in about:debugging got rid of this extra cpu usage.

about:debugging "Enable add-on debugging" checkbox in context

You could also turn off this add-on debugging in about:config. Set either devtools.chrome.enabled or devtools.debugger.remote-enabled - or both - to off.

For more see about:debugging - Firefox Developer Tools | MDN

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about:about will list the about pages which may help you.

Relevant to the specific question, as some mentioned already:

  • about:processes : Memory and CPU usage
  • about:performance : Energy Impact and Memory
  • about:memory --> Measure : In depth Memory analisis
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Do you have Flashblock or NoScript installed? Especially if not, I'd try to look into the flash-heavy tabs first. I've also seen lots of eBay tabs grind Firefox to a halt, albeit that was a while back (when I was actually using eBay).

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  • Yes to both, as well as ad-block plus. But there's still something that's periodically using CPU.
    – chris
    Jan 31, 2011 at 19:16
  • Then my next thought would be JavaScript-heavy sites that you allow through NoScript. Jan 31, 2011 at 19:38
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    This really should have been a comment as it obviously requires clarification from the OP.
    – Burgi
    Jul 1, 2016 at 7:39
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CPU Usage monitor addon served me well

enter image description here

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    How does it address the question, i.e. finding the particular tab?
    – ᄂ ᄀ
    Aug 13, 2018 at 16:49
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In Firefox's address bar, enter about:performance.

This will open Firefox's integrated Task Manager.

This task manager now includes, per tab (and extension), Energy Impact and Memory columns.

The Energy Impact column indicates which tab is using the most CPU resources. This is represented numerically, textually ("High" / "Medium" / "Low"), and graphically.

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