Clearing the Cache in Firefox Web Browser

For clearing the cache in Firefox, click on the Application Menu at the top right of the browser and select Settings, click on Privacy & Security, scroll down and look for "Cookies and Site Data" and click on "Clear Data.." button.

Just beside the Clear Data button you will see how much space the Firefox cache is occupying.

Your stored cookies, site data, and cache are 
currently using 167 MB of disk space.

When you click on Clear Data you will see a screen that will show how much space you will regain after clearing "Cookie and Site Data" as well as "Cached Web Content"

Click on clear to clear the cache!

✌️: Clearing all cookies and site data stored by Firefox may sign you out of websites and remove offline web content. Clearing cache data will not affect your logins.