Web developer can use it copy all cookies from any website to localhost. How to use it ? Open any website, then click the "Copy cookies to localhost" add-on, and click "Copy Cookies" button, you will see a message "Cookie copied". After this, you can open a localhost page, open firefox devtools, select "Application" tab. Under "Storage" - "Cookies" - "http://localhost:<your port>", you will find all cookies here.
