This targets an element, which does not work in cases where the thing you want to click is a button within a display screen element. Only use this if the game doesn't care where you're clicking, so long as it's on the screen.

Update: The site was poki.com. When I attempted to use the add-on on a clicker game there, it targeted the window the game was running on, but nothing happened after I selected the button in that window. It's possible that it's a kind of complex embedded player like Unity, like the dev response said, but the game doesn't say anything about that.