Close all option open Firefox windows and tabs. Open a new Firefox window. Now select the "Firefox" menu in the upper left-hand corner, then hover your mouse over "Options" until the drop-down menu appears and select "Options" from the drop-down menu.
Click on the "Privacy" tab if it is not already selected and then click on the "clear your recent history " link:
Uncheck all items except for "Cache" and set the time range to be cleared to "Everything"
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