Rated 5 out of 5 stars

Very useful, does what is says, and is unobtrusive. BTW, I don't agree at all with the two previous commenters:
1) The name is SINGLE key tab switch - you get what it says, and that's perfect.
2) A dialog is superfluous for keyboard users :-). It's a once-only setting anyway.
3) After opening links with middle clicks in new tabs, this addon lets you jump to them, SwiftTabs fails as long as the link is "selected".
Finally, a feature request: Two more keys, one for the first and one for the last tab. :-)