In Firefox 57-61, the progress bar is a thin line below the download arrow on the Downloads toolbar button. Do you have that button? On Windows, to show the classic menu bar (File, Edit, View...) you can tap the Alt key or press the F10 key.

Launch Free Download Manager by clicking its shortcut icon on desktop, after that, open Firefox browser. 4. A new tab opens in Firefox and asks to 'Add Free Download Manager extension', click 'Add', the extension will be installed.

I figured out when the download button came from.

I already use FDM, but ther are times when it doen not capture, so when the built in download manager is handling a download, I want to see the built in download manager progress dialog pop up.

when activated, interrupts the built-in download manager to direct links to FDM. Only with Firefox—Get Firefox Now ... Once the extension is enabled from the toolbar button

Firefox 57+ auto-hides the Downloads button on the Navigation Toolbar by default. The Download button should appear on the Navigation Toolbar once you open the Customize window. If you do not see the Download icon then click the Restore Defaults button to reset the layout in case you previously have moved this button. Once you see the Download button in customize mode then left-click this button to see the current auto-hide state and toggle its setting.

Is there an addon that will reveal the the built-in download manager in-progress window when a download is initiated?