Browser extensions are usually small software addons/modules that help to customize a web browser by offering a variety of often useful features such as advertisement blocking.
Unfortunately browser extensions can access private data such as the browsing history, bookmarks, password and other sensitive data. Moreover many programs have secretly installed browser extension to without the user’s knowledge. Other famous browser extensions have been infected by malware and adware often by malice from the developer(s) of the browser extensions.
I’m adding a list of articles and research related to browser extensions badness.
Feel free to edit this wiki post.
https://www.howtogeek.com/180175/warning-your-browser-extensions-are-spying-on-you/
https://www.ghacks.net/2018/05/11/googles-bad-track-record-of-malicious-chrome-extensions-continues/
https://www.ghacks.net/2016/11/01/browsing-history-sold/
https://palant.de/2019/10/28/avast-online-security-and-avast-secure-browser-are-spying-on-you/