I upgraded to Safari 13/ macOS 10.13.6 - and now, I cannot download extensions from the gallery. There doesn't seem to be a button from which to deploy any extension from the gallery anywhere. Does Safari not support extensions in this configuration?
The Safari 13 beta is out. It runs very nicely. What I didn't know is that there's a new extensions framework developers must use. Legacy extensions will not work at all, starting with Catalina. This is why the download links don't display. Bear that in mind if you upgrade.
The current version of Safari for OS 10.13.6 is 12.1.2. How did you get Safari 13? Can you install them in the Safe Mode?
Safe Mode - About
The "Install now" link is missing in Safari 13:
Problems downloading extensions in Safari 13
