Stylish extension disappears from Firefox and Chrome after data collection message

The Stylish browser add-on, which allows users to customize CSS, is no longer in the Mozilla and Google collections after a developer published an analysis in which he found that the extension is forwarding users’ browsing history.

Mozilla’s bug tracker states that the extension is disabled and that Firefox users who have installed it will see a warning. The page of the extension can no longer be called up in the Chrome Webstore and leads to a 404, which indicates that it has been removed. The extension has also disappeared from the Mozilla collection. The discussion in the bug tracker references a recent blog post by developer Robert Heaton, who took a closer look at Stylish.

Image of Heaton

In it, he writes that he found out that the extension sent his browsing history in combination with an identifier. This would allow SimilarWeb, which has owned Stylish since 2017, to trace browsing history to individual users. However, the company’s privacy policy would state that it only collects “non-personal information.”

SimilarWeb is an organization that collects information about traffic to websites in order to visualize visitor numbers, for example. According to Heaton, tracking could be turned off, but was on by default. The Register has asked SimilarWeb questions, but has not yet received a response.