I, as a thunderbird user, wish I could view the last downloaded files after their download, so that I do not have to open the file explorer and search for them to open them.
I almost always first download my attachments (to have them synchronised / organised in my cloud), and then open them to read them.
With Firefox, it is possible to reach the list of downloaded file, but I did not find an equivalent with thunderbird (sorry if it already exists).
* from the list of downloaded file, get an additional option: "view container mail"
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Tools > Saved Files
@waynesm: thank you for the hint! I think, that just a shortcut is missing to reach faster the overlay.