This so-called addon is nothing but Spyware (even for being here on Firefox its web doesn't load on Firefox but it does on Chrome). Stylus is much better and safe

this is spyware, use Stylus instead

Very limited selection of themes as the website is broken.
...the hello kitty youtube theme looked okay, but I wanted one with mroe pink, so I tried to search. It said "bad gateway". I will not return.

If You Use This Uninstall This Malicious Extension If You Want An Alternative Use Stylus

Ne fonctionne pas du tout et en plus quand on accède au site de l'extension le message bad gateway 502 s'affiche.

the extension steals or your browsing data.

Consider uninstalling the malicious Stylish extension. In 2016, with no input from the userbase, through some guy, pretending to be an independent developer, it basically was sold to a shady web analytics company, Similarweb. Since then, it is actively sharing your entire non-anonymized browsing history demo with them, assuming you ever clicked on one of the flashy "Agree" buttons. It initially did this without even asking for consent, and was banned from extension stores afterwards. Currently, it still breaks store policies, yet is not banned for unknown reasons. A safe alternative is Stylus.

Spyware

doesn't work

unofficial, prob spyware

This extension is a complete hoax. The homepage userstyles.org is not accessible with the Firefox browser. On all Chrome-based sites, userstyles.org is accessible without any problems. It's a shame how Firefox users are being fooled here.

Dead?