Fingerprinting
Browser fingerprinting identifies devices through a combination of screen, fonts, APIs, and behavior. Tor Browser unifies many of these traits so users are less distinguishable.
Browser fingerprinting identifies a device from the combination of traits its software exposes: screen and window geometry, installed fonts, timezone, language, canvas and WebGL rendering, supported APIs, and behavioral quirks. No single trait is unique, but the combination often is — and it persists across sessions without cookies.
Why it matters for Tor users
Tor hides the IP address, but a fingerprint can still link visits together and tie an onion session to a clearnet one. Tor Browser’s countermeasure is uniformity: every user gets the same window letterboxing, the same reported fonts and platform, and restricted APIs, so individual fingerprints dissolve into one large crowd.
Common mistake
Customizing destroys the uniformity. Extra extensions, custom themes, or an oddly sized window make a Tor Browser instance rare again — and rare is trackable. The Tor Browser setup guide warns against add-ons for exactly this reason. Fingerprinting is a deanonymization vector that works entirely above the network layer Tor protects.
Category: Security