Firefox Clear All History pop-ups with script

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What should I do when this happens after I clear the history in my web browser? "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. Script: chrome://browser/content/sanitize.js:136" I am not a computer tech, and I really do need the help of those who know how to fix this, my computer hangs whenever this pop-ups. Thanks in advance.