tl;dr: Browser fingerprinting—using hardware and software signals like GPU, CPU, fonts, audio processing, and canvas rendering—can uniquely identify users across sessions without cookies, VPNs, or incognito mode. Google, after years of delaying third-party cookie deprecation, now permits fingerprinting in its ad products, making it the de facto successor to cookies. Only Brave, Tor, and Mullvad Browser offer meaningful engine-level defenses; extensions and Firefox's protections help but can ironically make you more identifiable by being rare.