[Moter8]

Unfortunately:

>Sessions will not install on Safari 12 or later, as Apple has officially deprecated Safari Extensions.

[protomyth]

Which is being replaced by Safari App Extension Platform. Did I read it correctly that App Extensions can only be downloaded from the Mac App Store?

[gsnedders]

Yes.

[saagarjha]

Safari Extensions from the Safari Extension Gallery still work, but standalone ones don't.