Clearing recent history causes very long delay with message "a script has stopped responding"

When I take option to "Clear Recent History" from tools dropdown, there is a very long delay EVERY TIME, followed by this 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. Script: chrome://browser/content/sanitize.js:136 This happens even when Javascript has been disabled. This problem first appeared just after installing Firefox version 4.0 I can proceed to "Clear Recent History" only by again clicking that option after taking option to stop non responding script.