56!

In Firefox you can also middle click the reload button to duplicate the tab.

Edit: other things you can middle click:

• The back and forwards buttons: does, what the buttons do in a new tab, while duplicating the tab history.
• The new tab button: open a new tab directly after the current tab (and in the same container as the current tab).
• Items in the URL bar (such as autocomplete suggestions, the thing you just typed, or your frequent pages): opens them in a new tab (at the end though for some reason)

You can also Ctrl+click all of these for the same result.

Some pages try to re-implement links in javascript, but forget about anything other than left-click.

Edit: Don’t forget Ctrl+click. Works the same as middle click in most cases.

Yes, this is also the only implementation of this I could find. I’m not sure if the cinnamon js api is capable of something similar.