The research, conducted by Douglas Leith, a professor at Trinity College at the University of Dublin, looked at Google Chrome, Mozilla Firefox, Apple Safari, Brave, Microsoft Edge (the new Chromium-based version), and the Yandex Browser.

The most private browser was Brave, in the second Chrome, Firefox, and Safari, and in the third (least private) group lie Edge and Yandex.
Leith found Chrome, Firefox, and Safari all tagged telemetry data with identifiers that were linked to each browser instance. These identifiers allowed Google, Mozilla, and Apple to track users across browser restarts, but also across browser reinstalls.

Microsoft Edge and the official Yandex Browser were the worst as both used unique identifiers that were linked to the device's hardware, rather than the browser installation. Tracking users by hardware allows Microsoft and Yandex to follow users across installations and potentially link browser installs with other apps and online identities.

Edge collected the hardware UUID of the user's computer, an identifier that cannot be easily changed or deleted without altering a computer's hardware. Similarly,. Leith also found that Yandex transmitted a hash of the hardware serial number and MAC address to its backend servers.

The article also points out that Brave was the only browser that didn't use search autocomplete functionality to collect and send back information on a user's visited web pages, even though this can be disabled in Firefox, Chrome, and Safari, it's on by default.

Edge and Yandex "also sent back information about visited web pages that did not appear to be related to the search autocomplete feature, suggesting the browsers had other ways to track users' browsing habits".