Prevent the "Warning Unresponsive script" notice in FireFox by Extending the Time for the Script to Run

This error indicates 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.
To set Firefox to let the script run longer:
1. In the Location bar, type about:config and press Enter.
  The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise!, to continue to the about:config page.
2. In the about:config page, search for the preference dom.max_script_run_time, and double-click on it.
3. In the Enter integer value prompt, type 20.
    Press OK.
With scripts now allowed to run for longer times, you may no longer receive the prompt.
To reset the value:
1. In the Location bar, type about:config and press Enter.
    The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise!, to continue to the about:config
    page.
2. In the about:config page, search for the preference dom.max_script_run_time.
3. Right-click on it and choose Reset.
Source: http://support.mozilla.org/en-US/kb/Warning%20Unresponsive%20script