I'm guessing that it's palemoon's doing -- for some reason opening that page when a request is made to get the current url of the browser.
What used to be a very useful function, getting the current url of browser, has lately become one of the many victims of the (often justified) desire by browser makers to be paranoid about security.. So because of a concern that letting a 3rd party get the current url could be a security risk, it's becoming hard to get the current url of browser by a 3rd party tool. It's a reason that if you are primarily concerned with grabbing web page screenshots and need the urls for them included as meta info, you may need to use a browser addon.
However, i will certainly put palemoon on an exclusion list so that SC does not even attempt to get the browser url any longer.
i wonder if same thing happens with recent firefox screenshots..