How Firefox’s Enhanced Tracking Protection Blocks Trackers and When to Adjust It

Problem: Trackers still follow you even after you close a tab

When you visit a news site that loads social‑share buttons, embedded videos, or advertising scripts, those third‑party requests can set cookies or access storage long after you leave the page. This silent tracking builds a profile of your browsing habits without your explicit consent. The useful takeaway is that Firefox already ships a built‑in mechanism—Enhanced Tracking Protection (ETP)—that stops many of these requests before they reach the content process, and you can verify and tune it in a few clicks.

How ETP works under the hood

Firefox splits each tab into a content process that renders HTML, CSS, and JavaScript, and a privileged parent process that manages the UI and security policies. ETP lives in the content process, where it consults a periodically updated list of known tracker domains maintained by Disconnect.me. When a network request matches an entry, the content process blocks the request before any data is sent, which also prevents the tracker from setting cookies, accessing localStorage, or running fingerprinting scripts. Because the check happens early in the request pipeline, the performance impact is minimal compared to blocking after the page has already loaded.

ETP offers three preset levels:

• Standard – blocks known trackers in private windows only.
• Strict – blocks trackers in all windows and also blocks detected cryptominers and fingerprinters.
• Custom – lets you toggle cookies, tracking content, fingerprinters, and cryptominers independently.

The feature was introduced in Firefox 63 (2018) and has been enabled by default for all users since Firefox 69.

Worked example: verifying ETP on a tracker‑heavy site

1. Open Firefox and navigate to about:preferences#privacy. Confirm that Enhanced Tracking Protection is set to Standard, Strict, or a Custom configuration you prefer.
2. Visit a site known to embed many third‑party services, for example a news article that shows Facebook, Twitter, and LinkedIn share buttons.
3. Look at the address bar: a shield icon appears left of the URL. Click the shield to open a popup that lists the number of blocked trackers for that site (e.g., “Blocked 12 trackers”).
4. For a deeper check, open about:support and scroll to the “Application Basics” section. The line Enhanced Tracking Protection shows the active mode (Standard, Strict, or Custom).

These steps let you confirm that ETP is actively filtering requests without needing any external tools.

Trade‑off and limitation: when Strict mode breaks a site

Strict mode’s broad blocking can interfere with legitimate third‑party scripts that a site relies on for login, payment processing, or embedded content. For example, a banking portal that loads a fraud‑detection script from a domain also listed as a tracker may fail to authenticate, showing a blank login form or an error message.

To resolve this without lowering your global protection level:

1. Click the shield icon on the problematic site.
2. Select Disable protection for this site (or manage exceptions via about:preferences#privacy → Manage Exceptions).
3. Reload the page; the shield will now show a crossed‑out icon, indicating ETP is disabled for that domain while remaining active elsewhere.

Because the tracker list refreshes roughly every 48 hours, newly emerging trackers may not be blocked until the next update. If you notice a sudden increase in ads or tracking notices, checking the list version in about:support (under “Tracker Blocking List Version”) can confirm whether an update is pending.

Actionable closing: keep ETP working for you

Start by verifying the current mode in about:preferences#privacy. If you encounter site breakage, use the per‑site exception feature rather than lowering the global setting—this preserves protection for the majority of your browsing while fixing the specific issue. Periodically revisit the shield icon on sites you visit frequently to see how many trackers are being blocked; a rising count can indicate that the list is working, while a stagnant or zero count may merit a manual list update check. By combining the default Strict mode with targeted exceptions, you get strong privacy protection without sacrificing the functionality of the sites you trust.