Rated 2 out of 5 stars

My experience with Firefox 3.5.2 on the Mac:

Alt+Drag works! It duplicates the tab along with its history.

Ctrl+Drag doesn't work (instead it simply drags the tab to the new location).

From the address bar, neither Alt+Enter nor Ctrl+Enter work. Alt+Enter duplicates the current page to a new tab (but without the history), whereas Ctrl+Enter simply reloads the page.