https://arstechnica.com/information-technology/2018/05/chrome-and-firefox-leaks-let-sites-steal-visitors-facebook-names-profile-pics/

For more than a year, Mozilla Firefox and Google Chrome may have leaked users’ Facebook usernames, profile pictures, and likes if the users’ browsers visited malicious websites that employed a cutting-edge hack, researchers said Thursday.

The data could be extracted through what’s known as a side-channel vulnerability in the browsers’ implementation of new standards for cascading style sheets introduced in 2016. One of the new features known as the “mix-blend-mode” leaked visual content hosted on Facebook to websites that included an iframe linking to it and some clever code to capture the data. Normally, a security concept known as the same-origin policy forbids content hosted on one domain to be available to a different domain. The vulnerability was significant because it allowed hackers to bypass this bedrock principle for two of the Internet’s most widely used browsers.