Firefox may give you a “Warning: Unresponsive script” prompt that says “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.” This article describes why this could happen and possible solutions and workarounds.

This error is telling you that Firefox thinks that a script may be running out of control and would make Firefox hang if nothing is done. The script could be something on a web page you're accessing, in an extension you installed, or even Firefox itself.

Letting the script run longer

If you find that pressing the Continue button brings up the same dialog again, letting the script run longer won't help you; it will just make Firefox hang for longer. However, if you can use Firefox normally after pressing Continue, then the script may just need extra time to complete.

To tell Firefox to let the script run longer:

1. Type about:config in the address bar and press EnterReturn.
   A warning page may appear. Click Accept the Risk and Continue to go to the about:config page.
2. In the about:config page, search for the preference dom.max_script_run_time.
3. Click the Edit button and enter 20.
4. Press the checkmark button to save the preference.

With scripts now allowed to run for longer times, you may no longer receive the prompt.

If you still receive the prompt (or if you want to see it again), you should set that preference back to the default value.

1. Type about:config in the address bar and press EnterReturn.
   A warning page may appear. Click Accept the Risk and Continue to go to the about:config page.
2. In the about:config page, search for the preference dom.max_script_run_time.
3. Click the Reset button.

Error happens when accessing certain websites

If the error happens only on a specific website, you can block scripts from running on that website. Many sites still function even if scripting is disabled.

1. Install the JavaScript Toggle On and Off extension.
2. Click the menu button , click Add-ons and themes and select Extensions.
3. Find the JavaScript Toggle On and Off entry and click the OptionsPreferences button.
4. Scroll down to the Black-list text box and enter the URL of the site that's giving you problems.
5. Click Save. The domain name of the site will be added to the list.

Now that the problematic site has been blocked from running scripts, it will no longer cause unresponsive script warnings.

Other causes

An add-on could be causing the problem. See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems.

Based on information from Unresponsive Script Warning (mozillaZine KB)