Be careful with old versions!
These versions are displayed for reference and testing purposes. You should always use the latest version of an add-on.
--The Seperator tab is made smaller.(Thanks for Andrew Williamson)
--Start Firefox with page about:blank. Press Ctrl+T (Open new tab) and try this new opened tab close. You cannot.(Thanks for Pavel Cvrcek)
--select new active tab closest to the previous one, when closing one tab.
--one divide by zero error fixed