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First‑Party Isolation

Network Privacy

Privacy Browser Third‑Party Cookies Cookie Third‑Party Tracking

Browser privacy mechanism partitioning storage per first-party context.

Definition

First-party isolation (or storage partitioning) isolates cookies, cache, and other storage so third parties cannot share identifiers across different first-party sites.

In plain English Browser privacy mechanism partitioning storage per first-party context.

Why this matters

Why it matters: It blocks common cross-site tracking techniques and reduces linkability.

Example

Example: Third-party script gets a different storage partition on each site, preventing reuse of IDs.