Those prefix are great and I use them regularly!

Though imo the killer feature of FF address bar is simply that it's tied to a proper search history. Unlike chrome (which I sadly have to use at work), that only keep 90 days of history (!), making the address bar useless for anything but tabs, recent searches and as a link to a search engine. I really can't see an excuse for that behavior, the sqlite used by chrome is a few mb at worst.