try auto

Summary

Intent

The goal of this change is to remove the preference entirely from the Firefox codebase. This preference was used to optionally block (rather than partition) third-party tracker cookies and storage access when was set to (value 5). By removing it, the code is simplified so that trackers under are always partitioned rather than having a toggle to fully block them.

Solution

The changes span multiple layers of the codebase:

1. Preference removal: The static preference definition for is removed from , eliminating it from the preference system entirely.

2. Nimbus experiment feature removal: The Nimbus feature entry is removed from , along with its associated Nimbus integration test (), since the preference it controlled no longer exists.

3. Storage access logic simplification (): In both the window-based and channel-based storage access checks for , the code previously had separate branches for third-party trackers (which could either block or partition based on the pref) and non-tracker third parties (which were always partitioned). These are now unified into a single condition — both trackers and non-tracker third parties are treated the same way and always partitioned with .

4. Cookie service simplification (): The logic that chose between and rejection reasons based on the pref value is removed. When partition-foreign mode is active, tracker cookies are now always partitioned (with as the reason) rather than potentially fully blocked.

5. Test cleanup: The dedicated test file that tested blocking and allowing tracker cookies/storage/indexedDB based on the pref is entirely removed. References to the pref in other test files (, , ) are removed, and expected test outcomes are updated to reflect that trackers are now always partitioned rather than blocked. The runtime check that overrode expected blocking notifications based on the pref value is also removed.

6. Documentation update: The tracker cookie blocking entry is removed from the ETP (Enhanced Tracking Protection) matrix documentation generator ().