Restore File Download Prompt in Firefox

1. Launch the Firefox browser, and type about:config in the address bar; then hit Enter.
2. Confirm that you accept the risk and will be careful to open Advanced Preferences
3.  In the search box of Advanced Preferences, type browser.download.improvements_to_download_panel
4.  Double-click the found browser.download.improvements_to_download_panel option in the list to set it to false