Unless a person is using an adblocker, they are being tracked regardless of the browser they use. Every website contains "tracking pixels" that are hosted on sites that track visitors.
When you load a site, widget.com (fictitious site) in your browser, embedded in the html for that site are images (1x1 transparent pixel) that are hosted, not by widget.com but by separate site specifically for tracking visitors (eg. the person who loaded the page).
When you load a site, widget.com (fictitious site) in your browser, embedded in the html for that site are images (1x1 transparent pixel) that are hosted, not by widget.com but by separate site specifically for tracking visitors (eg. the person who loaded the page).