This document explains how to clear the cache and cookies from Mozilla Firefox 57.0 to the newest version
- Click the Menu (three stacked horizontal lines) then click Options.
- On the left side, select Privacy & Security, then select Clear Data....
- In the pop-up menu, make sure both boxes are checked for Cookies and Site Data and Cached Web Content, then click Clear.
NOTE: You can also clear cache and cookies using the legacy Clear Recent History menu by holding Ctrl + Shift + Del.