Firefox blocks common trackers in Private Browsing mode and in Enhanced Tracking Protection strict level to protect users’ online privacy. Some site functionality could be affected if the site relies on the blocked tracking script. Starting in Firefox version 142, to avoid site problems, Firefox has introduced WebCompat exceptions that unblock trackers under specific circumstances.

Web compatibility exception tiers

Firefox provides two tiers of web compatibility exceptions that balance privacy and site functionality at different levels.

• Baseline tier: The baseline exceptions target restoring critical website breakages, such as a broken site that does not load or major site functionality that is impacted.
• Convenience tier: Convenience exceptions restore website functionalities that are not strictly necessary for the site's primary purpose. For example, restoring missing images or allowing blocked video elements to load.

Where does Firefox apply web compatibility exceptions?

Firefox manages the WebCompat exception tiers to automatically align with the user's selected Enhanced Tracking Protection level.

• ETP Standard Level: Both tiers of exceptions are enabled by default in private browsing windows for a consistent browsing experience.
• ETP Strict Level:
  • Baseline web compatibility exceptions are enabled to maintain core website features.
  • The convenience exception tier is disabled to improve privacy.

How to configure web compatibility exceptions

To configure your settings for WebCompat exceptions:

1. In the Menu bar at the top of the screen, click Firefox and select Settings (select Preferences on older macOS versions).Click the menu button and select Settings.
2. On the left-side menu, select the Privacy & Security panel.
3. Go to the Enhanced Tracking Protection settings under the Browser Privacy section.
   • Two checkboxes of Enhanced Tracking Protection exceptions would be displayed in ETP: Strict and Custom levels.
4. Select or deselect the checkboxes to adjust Web compatibility exceptions.

Find the active ETP WebCompat exceptions

The ETP WebCompat exception list, detailing all deployed WebCompat exceptions and their corresponding Bugzilla bugs, is available at https://etp-exceptions.mozilla.org/. This website allows you to monitor and understand the rationale behind WebCompat exceptions on specific websites.

Related articles

• Enhanced Tracking Protection in Firefox for desktop
• How do I report a broken site in Firefox desktop?