I would love that if I open a new tab and surf to an url I have pinned already, that Firefox closes the new tab and navigate to the pinned tab of that url.
I often have a few news sites open, but have a habit of command+T'ing and type the site's url. After a while I figure I have a few tabs of the same website. I already have such a bad habit of having open too many tabs.
Safari on MacOS has this behaviour and it is way easier to keep down the number of tabs (When I try to record it, it for some reason stops behaving properly, so please take my word for it :)).