Unfortunately, since January 2017, Stylish has been augmented with bonus spyware that records every single website that I and its 2 million other users visit. Stylish sends our complete browsing activity back to its servers, together with a unique identifier. This allows it’s new owner, SimilarWeb, to connect all of an individual’s actions into a single profile. And for users like me who have created a Stylish account on userstyles.org, this unique identifier can easily be linked to a login cookie. This means that not only does SimilarWeb own a copy of our complete browsing histories, they also own enough other data to theoretically tie these histories to email addresses and real-world identities.
I bet the vast majority of Stylish users have no idea that this simple browser extension would not be scraping their browsing history and selling it to a scummy marketing technology company. I bet that most of them would not have explicitly agreed to such an obvious privacy intrusion. This is deeply unethical.