Firefox Shield Studies: How to Opt In or Out

Firefox Shield Studies are Mozilla’s way of testing experimental features and improvements on a subset of users before rolling them out to everyone. Opting in means you volunteer to receive these experiments; opting out stops them from being installed on your browser. This guide walks you through both processes, including how to check your current status and how to re-enable them if you change your mind.

What You’ll Need

• A current version of Firefox (the steps are the same on Windows, macOS, and Linux).
• Access to Firefox’s hidden configuration page (about:config) – no special tools required.
• If you are in an organization, your administrator may have locked these settings; you will see a warning if so.

Step-by-Step

Opting Out (Disabling Shield Studies)

1. Open Firefox and type about:config in the address bar, then press Enter.
2. Click the “Accept the Risk and Continue� button if a warning page appears.
3. In the search box at the top, type app.normandy.enabled. This is the master switch for Shield Studies.
4. You will see a preference with a toggle icon (a small arrow or pencil). Click the toggle or the pencil icon to change its value from true to false.
5. Next, search for app.normandy.api_url and double-click it. This preference holds the server address from which Firefox downloads studies. Clear the entire value (select all and delete) and leave it blank. This prevents Firefox from even checking for new studies.
6. Restart Firefox completely (close all windows and reopen).
7. To verify, go to about:studies in the address bar. You should see a message like “Studies are not enabled on this build� or an empty list. Any previously active studies will be uninstalled after the restart.

Opting In (Re-enabling Shield Studies)

1. Follow steps 1 and 2 above to open about:config.
2. Search for app.normandy.enabled and set it back to true.
3. Search for app.normandy.api_url. You need to restore the default value. The default is https://normandy.cdn.mozilla.net/api/v1. Type or paste this exactly, then press Enter.
4. Restart Firefox.
5. Go to about:studies to confirm that the page now shows “Studies are enabled� and that a list of available studies appears (it may be empty if no experiments are currently running).

Common Mistakes

• Only changing one preference: If you only set app.normandy.enabled to false but leave the API URL intact, Firefox may re-enable the setting on its own after an update. Always clear the API URL as well for a complete opt-out.
• Deleting the preference entirely: Right-clicking and choosing “Reset� is fine, but “Delete� can cause issues. If you delete app.normandy.api_url, Firefox may recreate it with a default value that you didn’t intend. Use “Reset� or set it to a blank string.
• Forgetting to restart: Changes in about:config often take effect immediately, but the study manager only runs at browser startup. Without a restart, you may still see active studies.
• Confusing Shield Studies with other telemetry: Disabling Shield Studies does not disable all data collection. Firefox has separate settings for telemetry and crash reports. If you want to stop all data sharing, you need to adjust those as well.

Tips

• Before opting out, consider that Shield Studies are typically low-risk and help improve Firefox for everyone. If you are only concerned about a specific study, you can remove it individually from about:studies by clicking “Remove� next to it, without disabling the entire system.
• If you are testing web pages or extensions and a study interferes, opting out completely is the cleanest solution.
• After opting out, you can still receive security updates and normal Firefox releases – you are not missing any stable features.
• If you ever want to re-enable studies later, the steps above are reversible. Keep the default API URL handy.

Troubleshooting

• Studies still appear after opting out: Make sure both preferences are set correctly (app.normandy.enabled = false and app.normandy.api_url is blank). Then fully quit Firefox (File → Exit, or Ctrl+Q / Cmd+Q) and reopen. If they persist, check about:studies – some studies may require a manual removal by clicking “Remove.�
• Can’t change the preferences: If the values are grayed out or you get a warning, your Firefox is managed by an enterprise policy. Contact your system administrator – you cannot override this from within the browser.
• Firefox updates reset my settings: Occasionally, a major update may reset app.normandy.enabled to true. After updating, re-check both preferences. You can also set app.normandy.enabled to false and then lock it by right-clicking and choosing “Toggle� – but locking is not officially supported, so it may not stick.
• Blank API URL causes errors: If you see error messages in the browser console about Normandy, that’s expected – Firefox is failing to connect to a server that isn’t configured. It’s harmless, but you can suppress it by setting app.normandy.logging.level to 0 (or just ignore it).
• Re-enabling doesn’t work: Double-check that you typed the API URL exactly as https://normandy.cdn.mozilla.net/api/v1 – a trailing slash or typo will prevent studies from loading. Also ensure app.normandy.enabled is true.

Frequently Asked Questions

What exactly is a Shield Study?

A Shield Study is an experiment Mozilla runs on a small percentage of Firefox users. It may change a UI element, test a new feature, or collect specific usage data. The goal is to validate ideas before a broader release.

Will opting out affect my normal Firefox usage?

No. You will continue to receive regular updates, security patches, and all stable features. You simply won’t be part of future experiments.

Can I opt out of individual studies without disabling all of them?

Yes. Go to about:studies, find the study you don’t like, and click “Remove.� That study will be uninstalled, but others will continue. However, new studies may still be offered to you.

Is opting out the same as disabling telemetry?

No. Telemetry is a broader data collection system. Shield Studies are a specific type of experiment. You can disable telemetry separately in Settings → Privacy & Security → Firefox Data Collection and Use.

How do I know if I’m currently in a Shield Study?

Type about:studies in your address bar. If studies are enabled, you’ll see a list of active and past studies. If you see “Studies are not enabled,� you’re not in any.

Are Shield Studies safe?

Mozilla reviews each study for privacy and security risks. They are designed to be low-impact and are automatically removed if they cause problems. However, if you prefer not to participate, opting out is a personal choice that is fully supported.

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