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

Extremely high cpu usage with no reason.

I love this so much. It saves my eyes from the radiation the WWW gives. I just wish there were more people using it!

Bug in add-on when using a private window.
Steps to reproduce:
In a browser with app not installed...
Open a new private window
Install the app from the add-on manager or userstyles website
Install theme from userstyles.org
Theme will not load when visiting designated site

Recomend use Stylus add-on instead

The idea is great, but the latest version uses HEAPS of CPU. The deployed version of the app doesn't match the one in the repository and there is no transparency despite a long history of privacy abuses. This whole project is an essay in the slow decay of communal resources, why we cannot have nice things etc.

This addon is garbage. Use Stylus instead. Unfortunately you will still have to deal with userstyles.org (the ones behind this extension) and that piss poor website.