When you click a link in your browser to navigate to a new website, the site you go on to visit holds the address of the site you arrived from, via the so-called “referrer-value”.
While this benefits websites know where visitors are coming from, it can also drip data about the personal browsing, because it tells the site the exact page you were viewing at when you clicked the link, said Mozilla.
Browsers also send a referrer-value when asking other details like ads, or other social media snippets combined in a modern website, which means this embedded content highlights also know exactly what page you’re revisiting. Sites record this referrer data and some sell it on to market site visitors to be targeted with ads.
In some cases, that referrer can leak highly sensible information. Researchers at the Electronic Frontier Foundation beforehand found one referrer from healthcare.gov also stated on data about the age and zip code of the user, along with whether they were a smoker or not, and their pay.
To stop this type of data leakage, from Firefox 59, the private browsing option will eliminate path information from referrer values sent to third parties, completely stripping out additional data and only leaving the web domain.
“This change limits site authors from inadvertently leaking user data to third parties when their users choose private browsing mode,” said Mozilla privacy engineer Luke Crouch.
Users can also adjust their default referrer options in Firefox. These will override the browser’s default referrer policy and neglect the site author’s referrer policy, putting the users choice first.
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