Stylish comes with turned on by default "Send anonymous data to Stylish developers" option. Author of this article says that collected data contains visited URLs. Which is not good for your privacy at all, and in some cases can be really disastrous.
Reddit thread on r/programming.

Thanks for that. After seeing this thread I found https://mastodon.social/@ben0_o/100309773118234802 and its recommendation of https://github.com/openstyles/stylus

(Though since I use Pale Moon as my primary browser I'm on the old-style Firefox addon, so I just disabled updates when the change originally happened--luckily I saw https://www.ghacks.net/2017/01/04/major-stylish-add-on-changes-in-regards-to-privacy/ at the time.)

I was using Stylish until now, thanks for mentioning this and also VanishedOne for an open source alternative.

Never heard of "Stylish" before but thanks for the information.

I think i should take a look at my toaster & refrigerator because you never know... Thanks for the heads-up and the interesting read.

I think I used it in the past. Way before 2017 so... I should be safe. :-P

deleted

A small bump just in case.

It's been removed (don't know if only temporarily or permanently) from Chrome webstore and Firefox addons pages.