Rated 5 out of 5 stars

Lightweight addon @4.1 kb

This addon provides an alternative solution to "tabfocus" prefs tweak implemented by mozilla

Both has a flaw :
Mozilla's implementation provides no way to use both kind of tabbing functionality ie 3 and 7
This addon's provides no single modifier key as shortcut ( similar to TabKey [modifier] by Mozilla )

Note : Single Key Shortcuts configured using keyconfig.xpi - does not work in input fields