Browser Monitors: How to enable 3rd Party cookies

HannahM — Wed, 10 Dec 2025 16:25:37 GMT

Summary: Since version 122, by default, Chromium blocks third party cookies. If a site needs these to run as expected, they will need to be enabled for the Browser Monitor.

Problem

The site to be tested does not load as expected with third party cookies blocked. This may be evident in the screenshots, as shown below, or the page may not load as expected.

Resolution

For local playback

There are two options for this:

Change the 'Block third-party cookies' setting in Chrome Incognito mode
1. Open an Incognito window
2. Move the Slider to disable blocking third party cookies
  
  This setting is persisted.
Allow third-party cookies for specific sites
1. In a Chrome Browser, navigate to chrome://settings/cookies
2. Add the domain for the site that is being tested.

For Private Synthetic Locations

The following Chrome startup parameter makes Chrome allow third party cookies for all websites by turning off the Chrome feature that blocks third party cookies:

--disable-features=TrackingProtection3pcd

From Cluster version 315 onwards

No changes are required, as the TrackingProtection3pcd feature will be disabled by default.

Note: if the private synthetic location configuration/ monitor configuration has previously been updated, as described in the 'Prior to Cluster version 315' section, then the lines added will need to be removed/ updated to allow the new feature list to be used.

Prior to Cluster version 315

Confirm the current list of disabled features.

in the vuc-browser.log of the Private Location search for --disable-features= and copy the whole value. For example, in Cluster version 313, it's
--disable-features=OptimizationGuideModelDownloading,OptimizationHintsFetching,OptimizationTargetPrediction,OptimizationHints,TFLiteLanguageDetectionEnabled,HttpsUpgrades,HttpsFirstBalancedMode
and you would copy
OptimizationGuideModelDownloading,OptimizationHintsFetching,OptimizationTargetPrediction,OptimizationHints,TFLiteLanguageDetectionEnabled,HttpsUpgrades,HttpsFirstBalancedMode
Add ,TrackingProtection3pcd to the end of the list of values. For example
OptimizationGuideModelDownloading,OptimizationHintsFetching,OptimizationTargetPrediction,OptimizationHints,TFLiteLanguageDetectionEnabled,HttpsUpgrades,HttpsFirstBalancedMode,TrackingProtection3pcd

Update the list of disabled features.

This feature can be disabled for all monitors running on the ActiveGate, or for a single monitor.

Note: These changes persist on update, so if new features are disabled by default, you may need to update your snippet.

To affect all monitors running on an ActiveGate

On the ActiveGate, open the user.properties file

- C:\\ProgramData\\dynatrace\\synthetic\\config\\user.properties on Windows
- /var/lib/dynatrace/synthetic/config/user.properties on Linux
Add the following line
com.ruxit.vuc.poolConfig.playerConfig.toRemoveStartupParams=--disable-features
On the following line, add the --disable-features snippet created earlier after com.ruxit.vuc.poolConfig.playerConfig.additionalStartupParams=--disable-features. For example
com.ruxit.vuc.poolConfig.playerConfig.toRemoveStartupParams=--disable-features com.ruxit.vuc.poolConfig.playerConfig.additionalStartupParams=--disable-features=OptimizationGuideModelDownloading,OptimizationHintsFetching,OptimizationTargetPrediction,OptimizationHints,TFLiteLanguageDetectionEnabled,HttpsUpgrades,HttpsFirstBalancedMode,TrackingProtection3pcd

To affect a single monitor

Open the Monitor> Settings> Recorded Clickpath
Select Script
Add the following snippet into the configuration section and update the value to be the snippet created earlier
, "experimentalProperties": [{ "name": "disable-features", "value": "OptimizationGuideModelDownloading,OptimizationHintsFetching,OptimizationTargetPrediction,OptimizationHints,TFLiteLanguageDetectionEnabled,HttpsUpgrades,HttpsFirstBalancedMode,TrackingProtection3pcd" }]
Save your changes

Resize issue view side panel.

What's next

If this does not resolve the issue, please open a support ticket and provide

a link to the affected monitor
mention this article and any other troubleshooting steps taken

What to read next:

Script mode for Browser monitor configuration
Synthetic Troubleshooting Map

Synthetic Browser Monitor Error Codes

article Browser Monitors: How to enable 3rd Party cookies in Troubleshooting