It's basically a spyware
https://robertheaton.com/2018/07/02/stylish-browser-extension-steals-your-internet-history/

Steals your browser history.

Violates privacy.

Spyware

Their privacy policy states they collect the following via this extension:

- Standard web server log information (i.e., web request) as well as data sent in response to that request, such as URL used, Internet Protocol address (trimmed and hashed for anonymization), TabID, HTTP referrer, and user agent; and

- Search engine results page data (keyword, order/index of results, links of results, title, description, and ads displayed).

https://userstyles.org/login/policy

THIS ADDON STEALS YOUR INTERNET HISTORY

https://robertheaton.com/2018/07/02/stylish-browser-extension-steals-your-internet-history/

It's basically a spyware
https://robertheaton.com/2018/07/02/stylish-browser-extension-steals-your-internet-history/

Was great in the past, but turned into spying tool! Use forked and clean Stylus!

This addon is a scam. Don't install it.

Privacy nightmare, steals user data, sends all sites visited to SimilarWeb, use stylus instead

Have used this is in the past, but I can't recommend it due to privacy issues. Recording my browsing behavior is not OK.

Abusive extension, collects user history.

This addon has been collecting browser history since January 2017. If you care about your privacy at all you should switch to Stylus instead.

This is nothing but spyware

Spyware

Sends all of your browsing history to a third party server.

Abusive and invasive add-on, which records and tracks all your navigation history.

Records all browsing history. Should be considered insecure, use an alternative.