nicknames cannot be used as tags since it doesn't support auto complete/filter by tag etc.
You should really check out FF tag system.Its really awesome.Vivaldi doesn't stand a chance.
https://www.youtube.com/watch?v=jRIyAu79OrM
Well, Vivaldi does support autocompletion of nicknames. Just tried it with HN (save it as a bookmark and add hn as a nickname)