Currently for a file being downloaded (incomplete, in-progress download), Firefox does not show the link or domain name from where the file is downloading. I would like to see this more easily.
Firefox currently offers the following:
1) Right-click -> Copy download link (or Go to download page). This can be pasted elsewhere to view but that is unpleasant.
2) After a download completes, the top-level domain name (TLD) is shown in the status line for the file in the Downloads library between the size and completion time.
For comparison, Chrome's Downloads manager shows the full download link for each file (completed or not). This link also works like a normal web link which is nice for consistency/discoverability, but not directly relevant to this suggestion.
For Firefox, showing the full link makes sense if a new status line is added for it (like Chrome). Otherwise, perhaps show the TLD after a separator after the progress text (same as completed downloads). Another possibility could be a tooltip mouseover but this isn't as useful. (Incidentally, Chrome eschews tooltips in the manager page.)
Note: my examples are from Windows.