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This document explains what cookies are, how they are used, and how you can gain control over the cookies stored on your computer by using the Cookie Manager in Mozilla Firefox.

What is a Cookie?

A cookie is a file created by an Internet site to store information on your computer, such as your preferences when visiting that site. When you visit a site that uses cookies, the site might ask Firefox to place one or more cookies on your hard disk.

Later, 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 also store personally identifiable information. Personally identifiable information is information that can be used to identify or contact you, such as your name, e-mail address, home or work address, or telephone number. However, a web site only has access to the personal information that you provide. For example, a web site cannot determine your e-mail address unless you provide it. Also, a web site cannot gain access to other information on your computer.

When you use the default cookie settings, this activity is invisible to you, and you won't know when a web site is setting a cookie or when Firefox is sending a web site its cookie. However, you can set your cookies optionspreferences so that you will be asked before a cookie is set. You can also restrict the lifetime of cookies to your current Firefox session.

Setting Up Cookie Rules

By default Firefox accepts all cookies, including cookies which would allow a site to recognize you effectively forever. If this doesn't suit you, you can tell Firefox to delete all cookies when you close Firefox:

  1. Click the menu button New Fx Menu Fx57Menu and choose Options.Preferences. , then select the Privacy panel.
  2. From the Keep until menu, select the I close Firefox optionpreference.

If you want to grant sites you trust the ability to store cookies permanently (e.g., to allow you to log in automatically to a site), click Exceptions…, enter the site address, and click Allow.

All the Settings

These are the optionspreferences that affect how cookies are managed by Firefox:

Accept cookies from sites: If you don't want any sites to store cookies on your computer, uncheck this optionpreference. Note that some sites may not work properly when cookies are disabled. If you want to grant certain sites the ability to store cookies, open the Cookies Exceptions window by clicking Exceptions…, enter the site address, and click Allow or Allow for Session.

Accept third-party cookies: If Firefox stores a site's cookie, it will return the cookie only to that particular site. Firefox will not provide one site with cookies set by another. Since a web site can only receive its own cookies, it can learn about your activities while you are at that site but not your activities in general while surfing the Web.

However, sometimes a web site displays content that is hosted on another site. That content can be anything from an image to text or an advertisement. The other web site that hosts also has the ability to store a cookie in Firefox, even though you haven't visited the site directly.

Cookies that are stored by a site other than the one you are visiting are called third-party cookies or foreign cookies. Web sites sometimes use third-party cookies with transparent GIFs, which are special images that help sites count users, track email responses, learn more about how visitors use the site, or customize your browsing experience. (Transparent GIFs are also known as web beacons or web bugs.) When this checkbox is not checked, it blocks these foreign cookies from being stored.

Keep until:

  • they expire
    If this optionpreference is selected, each cookie will be removed when the site that set it has determined the cookie should expire.
  • I close Firefox
    If this optionpreference is selected, cookies will be removed when you restart Firefox. Web sites requiring the use of cookies will still work, but if you restart Firefox, the web site will think that you logged into the site for the first time again.
  • ask me every time
    Display an alert every time a web site tries to store a cookie asking you if you want that cookie stored.

Accepting and Blocking Cookies

If you've chosen ask me every time from the Keep until menu, you'll see a dialog whenever a site tries to store a cookie on your computer providing the following options:

Allow: To allow this particular cookie, just click Allow. Use this if you trust the site. Allow for Session: If you want to allow this cookie for now, but have it deleted when you exit Firefox, click Allow for Session. Use this if the site doesn't work without cookies, but you don't want to have a permanent cookie stored for it. Deny: If you don't want this cookie to be stored, click Deny. Use this if you don't trust the site or suspect that it's compromising your privacy. Use my choice for all cookies from this site: Select this checkbox before clicking any of the buttons if you want Firefox to remember your decision and not ask again. The site will be added to the Cookie Exceptions window, where you can revert your choice should you wish to do so later.

The Cookies Exceptions Window


Access this window by clicking the Exceptions… button in cookies optionspreferences. Here you can make exceptions from your general cookies optionspreferences for specific sites. Using exceptions, you can allow all cookies, reject all cookies, or allow all cookies but have them deleted when you exit Firefox, regardless of your other cookie settings.

To add a site to this list, simply type the site's domain name in the field labeled Address of web site. Then click Block to reject cookies from the site, click Allow to allow cookies from the site, or click Allow for Session to allow cookies from the site but have them deleted when you exit Firefox.

To remove a site from this list, select it and click Remove Site. To clear the list completely, click Remove All Sites. This will clear the exceptions list so your general cookies optionspreferences apply.

The Show Cookies Window

Use the Show Cookies window to view and remove cookies. To access it, click the Show Cookies... button in cookies optionspreferences.

This window lists all cookies currently stored on your computer, grouped by site. You can expand the sites and select a cookie to display more information about it. You can also search for a site or a cookie name by typing in the search bar.

To remove a cookie from the list, select it and click Remove Cookie. To remove a site's cookies, select the site and click Remove Cookie(s). To wipe all cookies, click Remove All Cookies.

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