Private browsing
Private browsing is a feature in web browsers that enables users to access websites without the browser saving local records of browsing history, cookies, temporary files, search queries, or form data entered during the session.[1][2][3] Upon closing the private session, this data is discarded, preventing it from persisting on the device for later retrieval by the same or other users.[1][4] The mode is particularly useful on shared devices to avoid leaving traces of personal activity, such as on public or family computers, but it operates within the standard browser environment without altering network-level visibility.[5] A key limitation, often misunderstood, is that private browsing does not confer anonymity or prevent tracking by external entities: internet service providers, websites, employers, or governments can still monitor IP addresses, connection logs, and other network metadata, and no protection against malware or remote surveillance is provided.[5][6] This distinction underscores that while it enhances local privacy, reliance on private browsing alone for sensitive tasks can foster false security, as session data remains vulnerable to real-time observation and server-side logging.[5][6]Definition and Core Functionality
Technical Mechanisms
Private browsing modes achieve data isolation by employing session-specific storage mechanisms that prioritize volatile memory over persistent disk writes, ensuring that transient data such as browsing history, cookies, cache entries, and form data are not retained beyond the active session. Browser engines configure this isolation at the process or window level, preventing writes to standard profile directories or databases like history files, cookie stores, or indexedDB repositories. Upon session termination—typically triggered by closing all private windows or tabs—the in-memory data structures are purged without merging into the user's regular profile, thereby avoiding cross-session leakage.[7][8] In Chromium-based browsers, such as Google Chrome, incognito mode instantiates a temporary profile flagged with--incognito command-line parameters, which disables persistence for history (via the HistoryService), cookies (using a non-disk-backed CookieMonster instance), and cache (limited to RAM-based storage cleared on exit). This creates a sandboxed rendering process group separate from normal tabs, where site data remains accessible only within the incognito context to support functionality like logins but is discarded post-session to enforce non-persistence. Download history and explicit saves (e.g., files) may still occur unless user-configured otherwise, but automatic artifacts like autofill data are suppressed.[7][8]
Mozilla Firefox's private browsing leverages containerized windows with Gecko engine flags that route storage operations to ephemeral, memory-resident backends rather than SQLite databases (e.g., places.sqlite for history or cookies.sqlite for session cookies). Cache is handled via a temporary directory or in-RAM Necko cache, which is invalidated and deleted on private window closure, while extensions and plugins may be restricted or isolated to prevent state leakage. This approach extends to IndexedDB and localStorage, which are treated as session-only in private contexts, though third-party extensions can potentially bypass isolation if granted broad permissions.[1][9]
Apple Safari's Private Browsing mode similarly uses in-memory WebKit storage for cookies and history, avoiding updates to the persistent History.db and cookie jars, with cache confined to volatile partitions cleared at session end. Cross-browser commonalities include runtime isolation to mitigate intra-session tracking via partitioned storage, but variations exist in handling extensions or service workers, which may require explicit disabling for full isolation.[8]