downloaded items may be moved to other folders by dragging. after this, the open item and open containing folder actions are no longer responsive. however the item area or open icon still get lit as for responsive items. i think there should be some indication that the file was moved and that these actions are no longer available. alternatively, remember the new location and allow open item/folder in the new location

Bug 726451 is about the case where the file is removed, or moved using the operating system's file manager. I don't know if we can deal with the case where the file is moved by dragging the download item from the browser to the operating system's file manager. If we can detect the destination folder, then we could consider updating the download item to point to the new location.