Duplicating Tabs and Other Alt D Shortcuts

There is no direct tab duplication shortcut as of yet. There is however a trick you can use to duplicate your tabs with the keyboard

Alt + D + Enter
First, hold down the alt key. Then press "D" followed by enter.
Alt + D will select the current url in the address bar.
Alt + Enter will open a selected url in a new tab. (Alt + Enter with nothing selected will bring the window into fullscreen mode. This can be reversed with F11 or by pressing the keys again.)

Other
(Alt + D) + (Ctrl + C) will copy your current url.
(Alt + D) + (Ctrl + V) + Enter will paste a selected url into the bar and go

Alt + D + Backspace/Delete will clear the url bar. Useful to use as a quick search bar, as you don't have to take your hands off the keyboard. (You dont even have to press backspace, as once you start typing, it will clear any text already there.)