Sadly, it's not working for me.
Pressing [Alt]+[Shift]+D just opens the menu bar as if I was just pressing [Alt].

(using Firefox 99.0.1 on Windows 10)

I think it has something to do with localization. I use a german translation, where the "File" menu is called "Datei". So [Alt]+D opens that Dropdown for me ignoring [Shift].

It says in the description, that "Shortcut is configurable.", but I cannot find where.
//Update: I found it, thanks to the Screenshot. I'm just stupid. Sorry.

I changed it to [Alt]+[Shift]+K in manifest-json and created the extension myself for self-distribution.