A cookie is information stored on your computer by a website you visit. In some browsers, each cookie is a small file but in Firefox, all cookies are stored in a single file, located in the Firefox profile folder.
Cookies often store your settings for a website, such as your preferred language or location. When you return to the site, Firefox sends back the cookies that belong to the site. This allows the site to present you with information customized to fit your needs.
Cookies can store a wide range of information, including personally identifiable information (such as your name, home address, email address, or telephone number). However, this information can only be stored if you provide it - websites cannot gain access to information you didn't provide to them, and they can't access other files on your computer.
By default, the activities of storing and sending cookies are invisible to you. However, you can change your Firefox settings to allow you to approve or deny cookie storage requests, delete stored cookies automatically when you close Firefox, and more.
Cookie settings are managed in Firefox Options. To access these settings: