Unresponsive Script Warning

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When JavaScript code runs for longer than a predefined amount of time, you see a dialog that says Warning: Unresponsive Script. This time is given by the settings dom.max_script_run_time and dom.max_chrome_script_run_time. Increasing the values of those settings will cause the warning to appear less often, but will defeat the purpose: to inform you of a problem with an extension or web site so you can stop the runaway script.

Complete Error Message:

“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.”
Sometimes the message mentions an extension, which may or may not be causing the problem:
"Script: chrome://fastdial/content/storage.js:71"

Anything that causes the mozilla application to slow down can cause this warning to be issued. The slowdown may be caused by an extension, but it might also be a web page, another program, or resource utilization (CPU, memory, disk IO) at levels high enough to impact one or more application.

Finding the source of the problem

Click the Stop Script button on the warning dialog, then depending on your version, go to Tools > (Web Development) > Error Console. The most recent errors in the Error Console will identify the script that was running. But note, in some cases the add-on/extension causing the problem is not the one identified in the messages.


Unresponsive Script is often caused by a recently installed extension, or an update to the extension or application thus causing some incompatibility between the two.

Disabling extensions or rebuilding a new profile

Several techniques can be used to identify bad extensions. A quick test is to start in Safe mode. If it works better in safe mode, then start in normal mode and try disabling/uninstalling extensions to fix the problem - either one at a time, or in groups. To do this in groups, disable half of the extensions and if failure continues, disable the other half. Enable and disable addons in successively smaller groups until reduced to just one extension that fails. Or try creating a new profile. If the new Profile works correctly, then you can migrate specific files: [1] and reinstall extensions.

Some extensions reported having Unresponsive Script Errors

  • A9 Toolbar [2]
  • Adobe Reader (update Adobe Reader) [3]
  • AutoAdd (use QuickAdd instead) [4]
  • Extended Cookie Manager [5]
  • Fast Dial, delete the Fast Dial folder and reinstall [6]
  • Febe [7]
  • FoxyProxy when using GMail [8]
  • Gladder conflicts with UpdateScanner 3.0.4. When you open a page from UpdateScanner Firefox hangs for awhile[9]
  • Lazarus: Form Recovery, fixed in 3.0 see author's homepage if not yet at add-ons.
  • [Beta] Phoogle (Google) Map Mod 0.4.0 [10]
  • Media Player Connectivity [11]
  • MobWars scripts, try reseting your boss database. [12]
  • McAfee Spamkiller [13]
  • Unshorten v1.3 [14]
  • Yahoo Ask toolbar [15]
  • YouSendIt [16]


If you get the Unresponsive Script Warning on a specific web page, it could be a problem with the JavaScript on the web page. You may want to contact the webmaster of the site to inform them of the problem, or you may wish to file a Tech Evangelism bug report. Steffen Rusitschka suggests using setTimeout on web pages that need to execute JavaScript for long periods of time.

Updating Java

Updating Java seems to have helped the following pages. Note Java is not the same as JavaScript.

  • iCloud.com with Firefox 8 and "Find My Phone" [17] (Updated to Java Version 6 Update 30)

Webroot Spy Sweeper

The Webroot Spy Sweeper application can cause an Unresponsive Script Warning on certain web pages. Try disabling or uninstalling the application, then clear cookies for the related websites. [18]

Finding similar problems

Finding others with similar problems may find something that helps.

  • Google Groups search in last three months for script on page is busy
  • Google web search in last three months for script on page is busy

See also