Step1: Go to "Clear Recent History"
- On a PC, click the "Firefox" menu in the top left corner. Next,
select the right arrow next to "History" >> and click "Clear Recent
- Or press Ctrl+Shift+Delete to open the recent history window.
- On a Mac, from the Tools menu, select "Clear Recent History"
- Alternately, you can press Shift-Command-Delete.
Step2: Make sure "Details" is expanded, then select "Cache" from the list. Uncheck everything else.