This morning I downloaded DT again and installed (on top of the old installation). This brought the Safari Sharing and Quicklook extension back. When I activated the Safari extension I got a pop up saying something like
DT is an app downloaded from the Internet, etc etc. Are you sure you want to open it?
I don’t remember that I’ve gotten this pop-up for this extension previously. Let’s see if the extension remains after reboots of my machine. 