Safari’s extension ecosystem finally started being “good enough” for most users in the past couple of years, and now some of that momentum is being killed off. This feels like a really dumb move on Apple’s part. If you’re using an extension downloaded from the web-based Extensions gallery you’ve got some time, but will eventually need to find an alternative hosted in the App Store (likely by autumn 2019.) So what does this all mean? If you’re currently using an extension that you downloaded from the web it’s going to break in the fall, and you should find an alternative. Such extensions will still work with Safari 12, but being depreciated means it’s only a matter of time until support is dropped entirely, at which point only Safari App Extensions will work. Developers are encouraged to transition to Safari App Extensions. Submissions to the Safari Extensions Gallery will no longer be accepted after December 2018. safariextz-style Safari Extensions installed from the Safari Extensions Gallery is deprecated with Safari 12 on macOS. In plain English this means that extensions downloaded from the web, outside of the Extension Gallery and the App Store, will no longer work in Safari 12. And it doesn’t end there: Apple is depreciating support for extensions from the official Extensions Gallery: