Google and Mozilla have removed the Stylish browser extension from their respective add-on stores after the publication of a report this week that accused the extension of logging users' browser histories and sending the data to remote servers.
"We decided to block [Stylish] because of violation of data practices outlined in the review policy," said Mozilla software engineer Andreas Wagner in a bug report opened earlier this week.
The Stylish Firefox add-on page has been removed, while Mozilla plans to disable the extension in users' browsers and show a message explaining its decision.
Google did not give out any explanation, but the Stylish Chrome Web Store page now returns a 404 error.
The reason behind this sudden ban is a report authored by software developer Robert Heaton, published on Monday.
Heaton detailed Stylish' downward spiral since August 2016, when it was sold for the first time to another developer, who then sold it to infamous analytics firm SimilarWeb.
At the moment it was sold to SimilarWeb in January 2017, Bleeping Computer wrote about the uproar and privacy fears the sale announcement caused among the Stylish community. At the time, users reacted negatively to a new data collection practice that SimilarWeb announced for Stylish. The company said it would be collecting some analytics about users in order to determine user counts.
But on Monday, Heaton published screenshots taken with a network sniffing tool showing how the Stylish extension was collecting user browsing history and sending it to SimilarWeb's servers.
The extension is now gone, and the reputational damage following Heaton's report, along with Mozilla and Google's decision to remove it from their stores might be the final nail in its coffin.
Stylish has been a wildly popular extension for many years because it allowed users to use custom "styles" for web pages, allowing users to tweak the look and feel of any website to their liking.
When news of the SimilarWeb acquisition became public in January 2017, the open-source community forked the old Stylish project into a new one called Stylus, which works like the old extension but without the data collection code. Stylus is currently available for Chrome, Firefox, and Opera.