2 ways to prevent this problem (Score 1)

First you can go to preferences in safari and turn off "Open safe files after downloading". However what I did is add the folder action add - New item alert.scpt. Since widgets don't run till you go to dashboard and click on them, this will warn you the second one is added, you can then go to that folder and delete the widget. I think I am going to make my own script that will ask me if I want to keep the widget yes/no, and then delete the file if I say no. I really think apple should turn off auto install. You only need to double click a downloaded widget to install, so they don't need this added "convenience"