Firefox blocks known trackers to protect your privacy. In some cases, blocking trackers can also prevent parts of a website from working correctly. For example, a site might fail to load images, videos, login buttons or payment forms.

To reduce these problems, Firefox uses web compatibility exceptions in some Enhanced Tracking Protection (ETP) modes. These exceptions allow limited website resources that are necessary for a site to work properly while still keeping most tracking protections enabled.

This article explains what web compatibility exceptions do, how they affect privacy, and how to manage them in Firefox.

What are web compatibility exceptions?

Web compatibility exceptions are special rules maintained by Mozilla that temporarily allow specific blocked resources required for a website to function correctly.

Firefox only applies these exceptions in limited situations where tracking protection may otherwise break important website features.

Examples of website problems exceptions may help fix:

• Sign-in buttons that do not work
• Missing images or videos
• Payment or checkout failures
• Embedded content that does not load
• Websites that appear incomplete or broken

Firefox continues blocking many trackers even when exceptions are enabled.

How Firefox decides when to apply exceptions

Mozilla reviews reports of broken websites and creates targeted compatibility fixes when necessary.

These fixes:

• Apply only to specific websites or resources
• Are designed to restore functionality with minimal privacy impact
• Are maintained and reviewed by Mozilla
• Can be updated or removed as websites change

You can view the current list of deployed exceptions at https://etp-exceptions.mozilla.org/. This website allows you to monitor and understand the rationale behind web compatibility exceptions on specific websites, and also includes links to related Bugzilla reports for transparency and review.

Web compatibility exception levels

Firefox uses two levels of web compatibility exceptions.

Fix major site issues

This setting restores important website functionality when tracking protection causes serious breakage.

Examples include:

• Pages that fail to load
• Login or checkout problems
• Buttons that stop working
• Essential content missing from the page

Mozilla recommends keeping this setting enabled because it helps websites work properly while maintaining strong privacy protections.

Fix minor website issues

This setting restores non-essential website features that may be affected by tracking protection.

Examples include:

• Missing embedded videos
• Social media widgets
• Decorative images
• Embedded comments or media players

This setting may allow additional website resources compared to the major issues setting.

How web compatibility exceptions affect privacy

Web compatibility exceptions may allow some resources that Firefox would normally block.

However:

• Firefox does not completely disable Enhanced Tracking Protection
• Exceptions are limited to specific cases
• Mozilla reviews exceptions before deployment
• Most trackers remain blocked

Using stricter privacy settings may still cause some websites to work differently compared to other browsers.

If you prefer maximum privacy, you can disable some or all web compatibility exceptions. Keep in mind that doing so may cause websites to break or display incorrectly.

Where Firefox applies web compatibility exceptions

Firefox automatically adjusts exception behavior based on your Enhanced Tracking Protection level.

Standard Enhanced Tracking Protection

In Standard mode:

• Web compatibility exceptions are enabled in Private Browsing windows
• Firefox balances privacy and website functionality automatically

Strict Enhanced Tracking Protection

In Strict mode:

• Fix major site issues is enabled by default
• Fix minor website issues is disabled by default for stronger privacy protection

Custom Enhanced Tracking Protection

In Custom mode:

• You can choose which web compatibility exception settings to enable

Change web compatibility exception settings in Firefox for Desktop

1. Click the menu button and select Settings.
2. Select the Privacy and security panel.
3. Scroll to Enhanced Tracking Protection settings in the Browser Privacy section.
4. Select Strict or Custom.
5. Enable or disable:
   • Fix major site issues
   • Fix minor website issues

Change web compatibility exception settings in Firefox for Android

1. Tap the menu button .
2. Tap Settings.
3. Tap Enhanced Tracking Protection.
4. Select Strict or Custom.
5. Enable or disable the web compatibility exception settings.

What to do if a website still does not work

If a website still appears broken after enabling compatibility exceptions:

1. Reload the page.
2. Disable Enhanced Tracking Protection for the site temporarily.
3. Test the website in another browser.
4. Clear cookies and cache for the site.
5. Report the problem to Mozilla.

For more troubleshooting help, see Websites look wrong or appear differently than they should.

Related articles

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