It turns out that the Stylish browser extension is, since January 2017, basically spyware. Firefox has just blacklisted it. LWers who, like me, installed it at some point to experiment with Lesser Wrong or Greater Wrong CSS should seriously consider uninstalling it. There’s probably nothing you can do retroactively about having had every single URL you visited since installing Stylish sent off to SimilarWeb’s servers (and from there presumably to SimilarWeb’s customers).
It turns out that the Stylish browser extension is, since January 2017, basically spyware. Firefox has just blacklisted it. LWers who, like me, installed it at some point to experiment with Lesser Wrong or Greater Wrong CSS should seriously consider uninstalling it. There’s probably nothing you can do retroactively about having had every single URL you visited since installing Stylish sent off to SimilarWeb’s servers (and from there presumably to SimilarWeb’s customers).