As to your "problem", those are hyperlinks someone (you?) stored in your Dock. Either remove them via right-clicking on them or dragging them off. Or click on them to find out where they go to or where they are located in Finder.
OK: Last week i posted How to open PDF files not using Preview. The suggestion was to use Adobe Reader. So i changed it to open ALL in AR and that is what @ is. I changed it to Firefox and all of the icons changed to the Safari icon. I hope Preview does not came back.