My debug output is the same a gingerbeardman's:
[2017-11-16 15:11:23][input.keyword] Processing output of 'action.script' with arg ''
[2017-11-16 15:11:23][action.script] Processing output of 'action.script' with arg ''
Installed this workflow and I can use the hotkey to add unread bookmarks fine, and I can search for bookmarks fine also. However, when I use "pa", no window pops up for me to add a regular bookmark. In Safari, Develop -> Allow JavaScript from Apple Events, is checked. Safari is not blocking pop-up windows. What else am I missing?