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- Close all open Firefox windows and tabs. Open a new Firefox window.
- Click the Menu button in the top right
- Select the preferences "Options" button (Marked by a gear icon) - On Mac the button will say "Preferences" like below
- On the left select the Privacy tab
- Click "clear your recent history"
- A dialogue box will appear, select the items to delete - make sure that "Cache" is selected - and verify that the time range to clear is set to "Everything"
- Now click the "Clear Now" button
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