When GoldenDict enable scan popup functionality, if you want GoldenDict to show popup window, you need to select word by mouse and at same time press ALT or CTRL key. You can't show popup window only by mouse when needed.

Add a function, when a word was selected by mouse, nearby the word there will be a small flag, when you move mouse on the flag, popup window appears.

This function is copied from BingDict in window OS.