Tracking Cookies: What They Collect and How to Block Them
Some cookies keep you signed in. Others follow you from site to site. Here is the difference and how to stop the second kind.
By Siddharth ShankarUpdated October 20, 2026Third-party cookies are set by a site other than the one you are visiting, and are used to track you across websites. Firefox’s Enhanced Tracking Protection blocks cross-site tracking cookies by default, and the Strict setting blocks all cross-site cookies. Total Cookie Protection gives each site its own cookie jar. Blocking stops some tracking but not all, so combine it with other privacy settings.
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Cookies are small files that sites store in your browser. Most are harmless and useful, such as the one that keeps you logged in. The ones that raise privacy concerns are the cookies placed by other companies.
First-party and third-party cookies
- First-party cookies are set by the site you are visiting. They remember your login, your basket and your settings.
- Third-party cookies are set by a different site, often an advertiser or analytics service whose code is embedded in the page.
According to Mozilla’s support page on third-party cookies, these cookies are used for cross-site tracking. The same company can recognise you on many unrelated sites and build up a record of what you view.
What tracking cookies can reveal
A tracker may learn which pages you visit, what you search for, how long you stay and what you buy, tied to an ID stored in the cookie. Combined across many sites, that can suggest your interests, habits and more. This is data for advertising profiles, and sometimes it is sold or shared.
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How Firefox handles them
Mozilla says Firefox’s Enhanced Tracking Protection blocks cross-site tracking cookies by default. Its Strict mode blocks all cross-site cookies. Total Cookie Protection gives each site its own separate cookie jar, so a tracker cannot link your visits across sites.
How to block all cross-site cookies in Firefox
1Open Settings
Go to Settings, then Privacy and Security.
2Choose Enhanced Tracking Protection
Select the Custom setting.
3Pick Cookies
Tick the Cookies box and choose All cross-site cookies from the drop-down.
4Check the shield
Click the shield icon in the address bar to see what is blocked, or to turn protection off for a site that breaks.
Other browsers
Other browsers have their own cookie and tracking settings, and they use different names. Look under Privacy in your browser’s settings for options about third-party cookies and tracking protection. The labels change over time, so check the browser’s own help page.
The limits
Mozilla notes that blocking stops some tracking but not all. Blocking cookies can also break some sites, such as logins that rely on cross-site cookies or embedded content. Trackers also use other methods, such as browser fingerprinting, which cookie blocking does not touch.
How to see what is tracking you
Most browsers let you view the cookies stored for a site. In Firefox, the shield icon in the address bar lists the trackers it blocked on the page you are viewing. Looking at this for a few popular sites can be an eye-opener, because a single news page often loads trackers from many different companies.
Why sites use tracking cookies
Advertisers want to show relevant ads and measure whether they worked. Analytics firms want to count visitors. Social media buttons can recognise you even when you do not click them. None of this is necessarily malicious, but it means information about your browsing is collected by companies you never chose to deal with.
A sensible routine
- Use a browser setting that blocks cross-site tracking cookies, and keep the browser up to date.
- Clear cookies and site data from time to time, particularly after using a shared computer.
- Sign out of accounts you do not need to stay signed in to.
- Use separate browser profiles for work and personal browsing, so trackers cannot easily join them up.
Add more layers
Turn on the opt-out signal in Global Privacy Control, review what Google knows about you and see what someone can do with your IP address.
Sources
- Mozilla Support: Third-party cookies and Firefox tracking protection (definition, cross-site tracking, ETP defaults, Strict mode, Total Cookie Protection, steps, limits)
Frequently asked questions
What is a third-party cookie?
A cookie set by a site other than the one you are visiting, often used for cross-site tracking.
Does Firefox block tracking cookies by default?
Yes. Enhanced Tracking Protection blocks cross-site tracking cookies by default.
What does Total Cookie Protection do?
It gives each site its own cookie jar so trackers cannot link your visits across sites.
Will blocking cookies stop all tracking?
No. It stops some tracking, but other methods such as fingerprinting remain.
Can blocking cookies break websites?
Sometimes. You can turn protection off for a single site using the shield icon.
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