Go to the 'History' menu and select 'Clear Recent History'. A screen like this will pop up:
Please select 'Everything' from the drop-down list. Select the following options:
ALL the check boxes should be checked as shown above.
Finally click the clear now. The small window should disappear.
Once you have deleted your temporary files, please close all Firefox windows
and then reopen. If you still have an error, please email firstname.lastname@example.org with the error ID and your login name.