Firefox CPU usage: Difference between revisions

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Sometimes Firefox uses excessive amounts of CPU as reported by Windows Task Manager or by the ''top'' command on Linux.
This article describes how to prevent or work around high CPU usage in Firefox.


== Excessive CPU on certain web sites ==
==Only on specific pages==
If Firefox uses lots of CPU on certain web pages, please report the problem using Help -> Report Broken Web Site. Usually there's executable code on the site that is consuming the CPU. On the other hand, if a bug in Firefox is causing the excessive CPU usage, this will help track down the problem.
=== Plugins ===
If you're only having problems with sites that use [[Flash]] and updating to the latest Flash version doesn't help, you can use the [http://flashblock.mozdev.org/ Flashblock] extension to selectively enable or disable it [http://momentarypause.blogspot.com/2006/02/firefox-cpu-issues.html][http://forums.mozillazine.org/viewtopic.php?t=184258]


The Flashblock extension can help the problem by blocking Flash code that consumes excessive amounts of CPU.[http://momentarypause.blogspot.com/2006/02/firefox-cpu-issues.html][http://forums.mozillazine.org/viewtopic.php?t=184258]
If the problem happens when viewing PDF files in the browser using the [[Adobe Reader]] plugin, disable the Adobe Reader plugin  (see [[Issues related to plugins]] for details) and either use Adobe Reader as an external application, [https://support.mozilla.org/kb/disable-built-pdf-viewer-and-use-another-viewer use another PDF viewer] or else [https://support.mozilla.org/en-US/kb/view-pdf-files-firefox-without-downloading-them#w_using-the-built-in-pdf-viewer use the built-in Firefox PDF viewer].  


Sometimes JavaScript on some web pages can cause excessive CPU. You can use the NoScript extension to block execution of JavaScript on problematic pages.
=== JavaScript ===
Some sites can cause high CPU usage through extensive use of [[JavaScript]]. You can disable JavaScript selectively using the [http://noscript.net/ NoScript] extension.  


== Extensions ==
=== Report the site ===
Some [[problematic extensions]] can cause excessive CPU usage. See the linked article for which extensions cause this problem and possible workarounds.
Report the site using Help -> Submit Feedback. Reporting the problem will help identify sites with problems so Mozilla evangelists can help fix their problems, and also help Mozilla developers track down any bugs in Firefox that could be causing excessive CPU usage.


== Windows Compatibility Tab ==
==All the time==  
There are some reports that Firefox can cause excessive CPU usage if it's set to run in compatibility mode for an older version of Windows.[http://forums.scotsnewsletter.com/index.php?showtopic=13873] To fix the problem, right-click on the Firefox icon you click to start Firefox, click Properties, click the Compatibility tab, make sure the check box under Compatibility mode is unchecked, and restart Firefox.


== Adobe Acrobat ==
=== Extensions ===
Sometimes viewing pages with Adobe Acrobat can cause Firefox to use excessive amounts of CPU. This problem may be fixed by creating a WWW_OpenURL directory in the AdobeUM directory.[http://public.ok2life.com/welcome/index/54.html]
[[Problematic extensions]] can cause excessive CPU usage.


== Other causes ==
=== Windows Compatibility mode ===
* Read the [[Firefox hangs]] article for other solutions to Firefox consuming lots of CPU.
Firefox can cause excessive CPU usage if it's set to run in compatibility mode for an older version of Windows.[http://forums.scotsnewsletter.com/index.php?showtopic=13873] To fix the problem, right-click on the Firefox icon you click to start Firefox, click Properties, click the Compatibility tab, make sure the check box under Compatibility mode is unchecked, and restart Firefox.
* If none of the solutions on these pages fixes your problem, you may want to file a bug report. [https://bugzilla.mozilla.org/buglist.cgi?query_format=advanced&short_desc_type=allwordssubstr&short_desc=CPU&product=Core&product=Firefox&long_desc_type=substring&long_desc=&bug_file_loc_type=allwordssubstr&bug_file_loc=&status_whiteboard_type=allwordssubstr&status_whiteboard=&keywords_type=allwords&keywords=&resolution=---&emailassigned_to1=1&emailtype1=exact&email1=&emailassigned_to2=1&emailreporter2=1&emailqa_contact2=1&emailtype2=exact&email2=&bugidtype=include&bug_id=&votes=&chfieldfrom=&chfieldto=Now&chfieldvalue=&cmdtype=doit&order=Reuse+same+sort+as+last+time&field0-0-0=noop&type0-0-0=noop&value0-0-0= This] is a list of unsolved bugs in Firefox that cause excessive CPU usage. Look through the list, and if your situation doesn't match any of the situations listed, file a new bug report. If you cannot give a set of steps that reproduces the problem, you may want to try to [http://wiki.mozilla.org/MozillaQualityAssurance:Triage#How_to_Help_with_Regressions_--_Finding_Regression_Windows find a regression window] to determine which change to Firefox caused the problem. If you're running Windows, you may also want to use [http://www.microsoft.com/technet/sysinternals/utilities/ProcessExplorer.mspx Process Explorer] to determine which thread is using most of the CPU and include this information in the bug report.
 
=== Hardware acceleration ===
Disabling cursor and bitmap hardware acceleration on some video cards and drivers can reduce CPU usage when displaying images.[http://forums.mozillazine.org/viewtopic.php?p=2734282#2734282] To check hardware acceleration on Windows, right click on the desk top to get the display properties menu.  Then select Settings > Advanced > Troubleshoot. [http://www.deskshare.com/Resources/articles/dmc_turnoffhardwareacceleration.aspx This article] shows how.  For more detailed information on troubleshooting display properties, see [http://support.microsoft.com/kb/263039 this article.]
 
=== Windows prefetch ===
In  Windows XP and above, deleting the Windows prefetch files for Firefox (C:\Windows\Prefetch\FIREFOX*) can prevent problems with the jpeg_fdct_islow thread consuming lots of CPU. [http://forums.mozillazine.org/viewtopic.php?t=184258&start=309] Note: Automatic deletion of FIREFOX.EXE* prefetch files is planned for Firefox 15 ([https://bugzilla.mozilla.org/show_bug.cgi?id=692255 bug 692255]).
 
== See also ==
* [[Firefox hangs]]
 
==External links==
* [https://support.mozilla.org/kb/firefox-uses-too-many-cpu-resources-how-fix Firefox uses too many CPU resources - How to fix] (Firefox Support)


[[Category:Issues (Firefox)]]
[[Category:Issues (Firefox)]]
[[Category:Websites]]
[[Category:Websites]]
[[Category:Performance - Firefox]]
[[Category:Performance - Firefox]]

Latest revision as of 20:44, 8 May 2013

This article describes how to prevent or work around high CPU usage in Firefox.

Only on specific pages

Plugins

If you're only having problems with sites that use Flash and updating to the latest Flash version doesn't help, you can use the Flashblock extension to selectively enable or disable it [1][2]

If the problem happens when viewing PDF files in the browser using the Adobe Reader plugin, disable the Adobe Reader plugin (see Issues related to plugins for details) and either use Adobe Reader as an external application, use another PDF viewer or else use the built-in Firefox PDF viewer.

JavaScript

Some sites can cause high CPU usage through extensive use of JavaScript. You can disable JavaScript selectively using the NoScript extension.

Report the site

Report the site using Help -> Submit Feedback. Reporting the problem will help identify sites with problems so Mozilla evangelists can help fix their problems, and also help Mozilla developers track down any bugs in Firefox that could be causing excessive CPU usage.

All the time

Extensions

Problematic extensions can cause excessive CPU usage.

Windows Compatibility mode

Firefox can cause excessive CPU usage if it's set to run in compatibility mode for an older version of Windows.[3] To fix the problem, right-click on the Firefox icon you click to start Firefox, click Properties, click the Compatibility tab, make sure the check box under Compatibility mode is unchecked, and restart Firefox.

Hardware acceleration

Disabling cursor and bitmap hardware acceleration on some video cards and drivers can reduce CPU usage when displaying images.[4] To check hardware acceleration on Windows, right click on the desk top to get the display properties menu. Then select Settings > Advanced > Troubleshoot. This article shows how. For more detailed information on troubleshooting display properties, see this article.

Windows prefetch

In Windows XP and above, deleting the Windows prefetch files for Firefox (C:\Windows\Prefetch\FIREFOX*) can prevent problems with the jpeg_fdct_islow thread consuming lots of CPU. [5] Note: Automatic deletion of FIREFOX.EXE* prefetch files is planned for Firefox 15 (bug 692255).

See also

External links