It should be noted that there's a significant difference between Safari and Chrome in this respect, however. Safari content blockers are not actually JavaScript

It should be noted that there's a significant difference between Safari and Chrome in this respect, however. Safari content blockers are not actually JavaScript at all, they're nothing more than JSON rules, so content blockers have no webRequest API usage whatsoever. Whereas Chrome extensions are JavaScript, with webRequest capabilities. Safari Mac does have JavaScript extensions too (iOS only supports content blockers), and everything gorhill says does apply to them. And indeed some vendors ship both a content blocker and a Safari JavaScript extension in the same Mac app (though each one has to be enabled separately in Safari). Thus, it could be argued that this is a distinction without a difference. But from a technical perspective they're entirely different technologies. The macOS 10.15 SDK did add an API for a Safari JS extension to receive information from a content blocker embedded in the same Mac app, allowing for example the extension to show stats for blocked resources: https://developer.apple.com/documentation/safariservices/sfsafariextensionhandling/3238030-contentblocker https://developer.apple.com/documentation/safariservices/sfs... My personal theory is that Safari content blockers were designed primarily for iOS, which has no Safari web extensions, and the Mac side was a bit of an afterthought.