Hazel doesn't close tabs because it's 'like a trip down memory lane.' Mozilla says it has some profile and tab group features coming later this year that might help her organize those memories.
How is that a "power user"? That's just a poor way to use the browser. It's basically just 7400 bookmarks in one long list; you can't even group/nestle book marks on Firefox.
A power user would use something called "bookmarks" to organise that better.