Works like a charm, well done!

It is strange to me that there is no built in tab duplication shortcutkey. This adds one and it works. Thank you.

Works fine on Android.

Sadly, it's not working for me.
Pressing [Alt]+[Shift]+D just opens the menu bar (while still holding and not releasing yet) as if I was just pressing [Alt] (after releasing it).

(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].
Same for [Alt]+[Shift]+A, which opens the "View" dropdown ("Ansicht" in german).

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

//Update: Don't mind me, I'm stupid. Since I hardly use any addons, I did not know of the settings area, where I can configure shortcuts for addons. Sorry.
For everybody as stupid as me: on your browsers addons page there is a gear icon. Select "manage extension shortcuts" (at the bottom) and configure to your hearts content.

Works fine! If enable search by keyword then can't change default shortcut combination. You can copy and paste required char ctrl+c ctrl+v to resolve this problem.

Shortcut does not work. Default doesn't work, and customized combinations don't work too.

Windows NT 10.0; Win64; x64; rv:61.0

2018/8/24 2:54:52(JST)
When I pressed ctrl + shift + D (default), "Bookmark All Tabs" is triggered.
But I noticed this extension cannot override default shortcuts. After I changed the combination to Alt + K, it works.
I think default combination should be changed.

I really wish I could integrate it into the Address Bar :(
like: (Enable Right Click and Copy )
https://addons.mozilla.org/en-US/firefox/addon/enable-rightclick-and-copy/

10/10 :D
Absolutely LOVE IT

FF 60.0.1 macOS High Sierra. Thank you Skeletonxf!

Can you add an option to duplicate tab in another container?