Please accept my apologies for my vague answer regarding the Tabbed Browsing add-on. When I upgrade my browser over time, the add-ons which I've kept and made compatible seem to be part of the new installation although in fact they aren't. It's easy to forget that.
This extension is an enhancement for the basic tab controls provided in Firefox. It replaces the existing user interface with a new, more visible user interface, and also includes UI for other hidden features that are part of the browser, as well as features provided explicitly by the extension.