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This repo serves as a staging area for shavar / tracking protection lists prior to production deployment to Firefox. This repo gives Mozilla a chance to manually review all updates before they go live, a fail-safe to prevent accidental deployment of a list that could break Firefox.

Not all domains in this repository are blocked in all versions of Firefox. The master branch represents the base list blocked by Nightly. Beta, release, and past versions of Firefox all use versions of this list, accessible as branches of this repository. We may also unblock certain domains through our anti-tracking interventions temporarily when we discover site breakage. These temporary exceptions are tracked in Bug 1537702, and the policy governing their use is described below.

These lists are processed and transformed and sent to Firefox via Shavar.

Disconnect's Lists

Firefox's Enhanced Tracking Protection features rely on lists of trackers maintained by Disconnect. Mozilla does not maintain these lists. As such, we will close all issues and pull requests related to making changes to the list contents. These issues should be reported to Disconnect.


A version controlled copy of Disconnect's list of trackers. This blocklist is the core of tracking protection in Firefox.

A vestige of the list is the "Disconnect" category, which contains Facebook, Twitter, and Google domains. Domains from this category are remapped into the Social, Advertising, or Analytics categories as described here. This remapping occurs at the time of list creation, so the Social, Analytics, and Advertising lists consumed by Firefox will contain these domains.

Firefox consumes the list as follows:

  • Tracking: anything in the Advertising, Analytics, Social, Content, or Disconnect category. Firefox ships two versions of the tracking lists: the "Level 1" list, which excludes the "Content" category, and the "Level 2" list which includes the "Content" category.
  • Cryptomining: anything in the Cryptomining category
  • Fingerprinting: anything in the FingerprintingInvasive category. By default, ETP's fingerprinting blocking only blocks Tracking Fingerprinters, that is domains which appear in both the FingerprintingInvasive category and one of the Tracking categories. Firefox does not use the FingerprintingGeneral category at this time.


A version controlled copy of Disconnect's list of entities. ETP classifies a resource as a tracking resource when it is present on blocklist and loaded as a third-party. The Entity list is used to allow third-party subresources that are wholly owned by the same company that owns the top-level website that the user is visiting. For example, if owns and is on the blocklist, it will not be blocked on Instead, will be treated as first party on, since the same company owns both. But since is on the blocklist it will be blocked on other third-party domains that are not all owned by the same parent company.

Other lists

In addition, Mozilla maintains several lists for Firefox-specific features and experiments. The lists currently in active use are:

  • social-tracking-protection-blacklist.json: a subset of trackers from Disconnect's blocklist. This list is used to identify "social media" trackers within Firefox's UI. All of the origins on this list should also be included in Disconnect's disconnect-blacklist.json list.

List Versioning and Release Process

As of Firefox 72, all desktop releases use versioned blocklists, i.e., each version of Firefox uses a version of disconnect-blacklist.json and disconnect-entitylist.json specific to that version. These versions are tracked by branches of this repository. For the current cycle (Dec. 2019) this means there is a 73 list (Nightly), a 72 list (Beta), a 71 list (Release), and a 68 list (ESR).

Nightly uses a staging version of the blocklist; the staging blocklist pulls in changes from Disconnect as soon as they are available. When a new version of Firefox is released, we will also release a new version of the list that corresponds to the version of Firefox moving from Nightly (main branch) --> Beta (versioned branch). That version of the list will ride the trains along with its respective Firefox version. Releases older than Firefox 69 use the 69 version of the blocklist.

This means that all changes will be tested for at least the full beta cycle and part of the Nightly cycle. We may choose to shorten the testing cycle in the future.

There are three possible exceptions to this process:

  1. Fast-tracked changes which are deployed immediately to all channels
  2. Temporary exceptions which are deployed using Remote Settings
  3. List freezes for when we’d like to test changes for a longer duration. These are tracked in Github issues on this repository.

Fast-tracked changes

We will fast track breakage-related updates or policy-related updates, both of which may only be done by Disconnect. Fast-tracked changes should have minimal, if any, risk of breakage.

Changes that may be fast-tracked include:

  • Deleting a domain from the blocklist and its respective domains from the entity list.
  • Adding new domains to the entity list.
  • Replacing a domain currently on the list with a new domain at the request of the company that owns the domain. These requests must go through Disconnect.
  • Moving a domain between list categories of the same feature.

As soon as Disconnect makes changes of this type we will merge them into each versioned list and deploy them across all channels.

Temporary exceptions

We may choose to grant a temporary domain-based exemption in response to website breakage as detailed in our anti-tracking policy.

List freezes

We may want to let certain changes bake in our pre-release browsers for a couple extra cycles. This provides more time for us to discover user-reported breakage or run breakage studies on the lists. In these cases we may hold back the changes from moving to a new release of Firefox. These freezes will either apply to the entire blocklist, or to specific categories of the blocklist (e.g., we shipped cookie blocking for the Level 1 list while we further tested the Level 2 list). We will not freeze specific domains or commits.

List update process

This repo is configured with Travis CI builds that run the scripts/ script to verify all pull request changes to the list are valid.

This Travis CI status check must pass before any commit can be merged or pushed to master.

Making changes to the format

When making changes to the list formats, corresponding changes to the scripts/ script must also be made.

To help validate the validator (such meta!), use the list fixtures in the tests directory. Run the script against a specific file like this:

./scripts/ -f <filename>
  • tests/disconnect_blacklist_invalid.json - copy of disconnect-blacklist.json with an invalid "dnt" value
  • tests/disconnect_blacklist_valid.json - copy of disconnect-blacklist.json with all valid values
$ ./scripts/ -f tests/disconnect_blacklist_valid.json

tests/disconnect_blacklist_valid.json : valid

$ ./scripts/ -f tests/disconnect_blacklist_invalid.json

tests/disconnect_blacklist_invalid.json : invalid
Facebook has bad DNT value: bogus


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