User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:56.0) Gecko/20100101 Firefox/56.0 Build ID: 20170903140023 Steps to reproduce: 0. Make sure you are set to 'Remember my browsing and download history' and history isn't cleared when you close Firefox. 1. Complete a download. 2. Close Firefox. 3. Delete / move that downloaded file. 4. Start Firefox. Open Library button > Downloads subview. Actual results: The panel doesn't know that this file has been deleted. If you now open the Library window > Downloads and select this missing file (if it was the latest downloaded file, it would automatically be selected), its status changes to 'File moved or missing', both in the Library window and in the Library button. Expected results: Firefox should say 'File moved or missing' and not let me try and open the file or its folder.