This feature already exists and you don't need a button for it. It's part of HTML metadata, specifically the <link rel="shortlink"> tag. You could either provi

This feature already exists and you don't need a button for it. It's part of HTML metadata, specifically the <link rel="shortlink"> tag. You could either provide some sort of button to your browser to place this into the clipboard, or use an extension like pentadactyl to add a keyboard shortcut for it. (It's simply “y” by default - so copying URLs works like yanking in vim)