Cookies are a piece of your data that a website receives each time you visit it.
Used to : authentication, storing personal preferences, user settings, tracking the status of the access session, collecting statistics, etc.
If you do not want sites to collect any data about you , then in Firefox you can disable the collection of Cookies:
1. Go to “Settings -> Privacy & Security”.2. Under “Enhanced Tracking Protection”, select “Personal” to choose what to block.
3. Check the box “Cookies”.
4. Select the mode “All Third Party Cookies”.