How to clear the Firefox cache

Click the menu button and select Settings.
Select the Privacy & Security panel.
In the Cookies and Site Data section, click Clear Data….
Remove the check mark in front of Cookies and Site Data.
- For more information about managing site data, see Manage local site storage settings.
With Cached Web Content check marked, click the Clear button.
Close the about:preferences page. Any changes you've made will automatically be saved.