https://arstechnica.com/information-technology/2018/07/stylish-extension-with-2m-downloads-banished-for-tracking-every-site-visit/

Google, Mozilla, and Opera have pulled a browser extension with more than two million downloads after it was caught tracking every website its users visited—and sending the data to a remote server.

The Stylish extension allowed users to customize the look and feel of websites in a variety of ways. Among other things, it could remove clutter such as Facebook or Twitter news feeds, change normal pictures to black-and-white manga images, and change black-on-white site themes to white-on-black themes. Starting this year, Stylish started performing these useful functions at a high price: according to software engineer Robert Heaton, the extension started sending users’ complete browsing activity back to its servers by default, along with a unique identifier that in many cases could be used to correlate email addresses or other Internet attributes belonging to those users.