Across browsers it works only if both browsers are based on the same engine. - Group1: Chrome, Chromium, Opera, ... - Group2: Firefox, Tor Browser, ... - Gro

Across browsers it works only if both browsers are based on the same engine. - Group1: Chrome, Chromium, Opera, ... - Group2: Firefox, Tor Browser, ... - Group3: on iOS every browser is based on Safari - ... Though with a backend you could track users switching among Chrome and Firefox by misusing WebRTC to leak the private IP ( https://www.perfect-privacy.com/webrtc-leaktest/ https://www.perfect-privacy.com/webrtc-leaktest/ ). If the switching between browsers happens in a short period of time, the public + private IP is a pretty solid guess. If you observe and store this connection once you can always track the user switching among the two browsers.