Good, but... Rated 4 out of 5 stars
... I can only get 2 of the options to show up on the context menu: 'Sort tabs by URL' and 'Sort tabs by title'. The rest, including 'Close duplicates' will not show up in the menu no matter what I try.
I'm using Firefox 7 on Windows 7 Home Premium 64-bit, should any of that matter.