<https://www.scss.tcd.ie/Doug.Leith/pubs/browser_privacy.pdf> Abstract We measure the connections to backend servers made by six browsers: Google Chrome, Mozilla Firefox, Apple Safari, Brave Browser, Microsoft Edge and Yandex Browser, during normal web browsing. Our aim is to assess the privacy risks associated with this back-end data exchange. We find that the browsers split into three distinct groups from this privacy perspective. In the first (most private) group lies Brave, in the second Chrome, Firefox and Safari and in the third (least private) group lie Edge and Yandex. [...] VIII. CONCLUSIONS We study six browsers: Google Chrome, Mozilla Firefox, Apple Safari, Brave Browser, Microsoft Edge and Yandex Browser. For Brave with its default settings we did not find any use of identifiers allowing tracking of IP address over time, and no sharing of the details of web pages visited with backend servers. Chrome, Firefox and Safari all share details of web pages visited with backend servers. For all three this happens via the search autocomplete feature, which sends web addresses to backend servers in realtime as they are typed. In Chrome a persistent identifier is sent alongside these web addresses, allowing them to be linked together. In addition, Firefox includes identifiers in its telemetry transmissions that can potentially be used to link these over time. Telemetry can be disabled, but again is silently enabled by default. Firefox also maintains an open websocket for push notifications that is linked to a unique identifier and so potentially can also be used for tracking and which cannot be easily disabled. Safari defaults to a choice of start page that potentially leaks information to multiple third parties and allows them to preload pages containing identifiers to the browser cache. Safari otherwise made no extraneous network connections and transmitted no persistent identifiers, but allied iCloud processes did make connections containing identifiers.

From a privacy perspective Microsoft Edge and Yandex are qualitatively different from the other browsers studied. Both send persistent identifiers than can be used to link requests (and associated IP address/location) to back end servers. Edge also sends the hardware UUID of the device to Microsoft and Yandex similarly transmits a hashed hardware identifier to back end servers. As far as we can tell this behaviour cannot be disabled by users. In addition to the search autocomplete functionality that shares details of web pages visited, both transmit web page information to servers that appear unrelated to search autocomplete.