There are no working tab group addons post XUL, I've tried them all and they are all completely broken. While I agree that you shouldn't run without updates, please don't tell people that there is a working substitute for this functionality.
Before posting that comment, I searched not only for such addons but for the last updates to those addons and for reviews of those addons, which seemed to suggest that they work as Web Extensions and function as at least some people want. That said, I can't vouch for them personally, and I appreciate you providing some firsthand experience.
