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At times, Firefox may require significant CPU resources in order to download, process, and display web content. If you are experiencing periods of sustained high CPU usage while using Firefox, this article presents some options for you to review.

  • The CPU (Central Processing Unit) is the "brain" of the computer. When the CPU is being heavily used, the overall performance of the computer can be impacted.
  • Depending on your operating system, you can review and monitor CPU usage through specific tools. On Windows, the Performance tab of the Windows Task Manager displays the rate of CPU consumption.

Table Of Contents

Only on specific pages

If high CPU usage occurs only while visiting specific web sites, the following areas should be reviewed to identify the common issue.

Plugins

Flash

Some web sites, such as YouTube, require a plugin called Flash. The Using the Flash plugin with Firefox plugin is used to display animated or video content inside the web browser window. This plugin is updated regularly, and some sites require the latest version of the plugin to be used.

  1. Download and install the latest version of the Using the Flash plugin with Firefox plugin For more information, see Using the Flash plugin with Firefox.
  2. A Firefox add-on, called Flashblock, allows you to selectively enable and disable Using the Flash plugin with Firefox content on web sites.

Adobe Reader

The Using the Adobe Reader plugin with Firefox plugin enables the display of PDF documents inside the Firefox browser. The plugin is the browser component of Adobe Acrobat Reader, a free tool for reviewing and printing PDF documents. If the problem seems to be occurring when you access PDF documents:

  1. Try updating Adobe Reader. For more information, see Using the Adobe Reader plugin with Firefox.
  2. You can configure Firefox to open PDF documents outside of Firefox. For more information, see open PDF documents outside of Firefox.

JavaScript

JavaScript is a scripting language that is included in many web pages to enhance the experience with menus, sounds, and other features. In an individual site, extensive use of JavaScript may require significant CPU usage. A Firefox add-on, called NoScript, allows you to selectively disable JavaScript on web sites. For more information, see NoScript.

  • You can also selectively enable and disable types of JavaScript actions, which may affect performance. For more information, see JavaScript.

Report the web site

If you are unable to determine the source of the problem with a specific site, you can report the site to the Firefox development team, which can review the site to determine if there are specific issues in Firefox that need to be addressed.

  • To report a web site, at the top of the Firefox window, click the Help menu, and select Report Broken Web Site....

Note: No personal information is required to submit a report of a broken web site. Reporting issues with specific web sites assists the Firefox team in improving the browser.

On every web site

Extensions

Extensions for Firefox are developed by a community of thousands of individuals spread around the world. These individuals are responsible for the content of their extensions. Sometimes, CPU usage problems can occur due to varying development standards, incompatibility between extensions, and insufficient support for newer versions of Firefox. For more information, see Troubleshooting extensions and themes.

Hardware acceleration

Disabling cursor and bitmap hardware acceleration on some video cards and drivers can reduce CPU usage when displaying images. For more information, see the documentation that came with your video card.

Windows:

Windows Compatibility mode

Windows Compatibility mode enables the execution of Windows program in an environment that mirrors earlier versions of the operating system. For example, you can execute Firefox in a Windows XP environment that is running the program as if the operating system was Windows 95.

Running Firefox on Windows in Compatibility mode has been known to cause high CPU usage. To stop Windows from running Firefox in Compatibility mode:

  1. Find the firefox.exe file. Typically, this file is located here:
    C:\Program Files\Mozilla Firefox
  2. Right-click the Firefox icon, and select Properties to open the Mozilla Firefox Properties window.
  3. Select the Compatibility tab, and make sure Run this program in compatibility mode for: is deselected.

Windows prefetch

Newer versions of Windows utilize a mechanism to accelerate the boot process. On Windows XP and Vista systems, the operating system must load many individual pieces of files during the boot-up process for the operating system and applications. Windows maintains a record of the pieces that are loaded during the boot process in a folder. Subsequent rebooting can use this trace to identify files that would be more efficient to load entirely at one time, instead of loading individual pieces across multiple reads of the hard disk. This prefetch mechanism can accelerate the overall performance of the computer.

However, the method of deciding which files to load may not be efficient for Firefox and can require significant CPU resources. You may experience faster performance by removing prefetch files on Windows XP or Windows Vista systems. The prefetch files are stored here:
C:\Windows\Prefetch\

Delete any filename beginning with: FIREFOX




Based on information from Firefox CPU usage (mozillaZine KB)


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Page last modified on Friday 30 of May, 2008 10:03:12 PST.
Contributors to this page: Chris_Ilias , Bo , AliceWyman , djstsys and skulvis .
- This is a support/troubleshooting article -