I read this article https://wiki.mozilla.org/NPAPI:HttpOnlyCookies , since the article is almost two years old, has it been implemented in NPAPI or Firebreath
It's not listed as an accepted proposal on the main NPAPI page, so it's never become part of NPAPI. That's why it's not in the NPAPI headers. Given that, it's unlikely any browser implements it. Chromium certainly hasn't, and mxr doesn't show any indication of NPNURLVHttpOnlyCookie in Gecko either. (Not surprising, since both Chromium and Mozilla contributors argued against it on the NPAPI list when it was proposed.)
The age of the proposal is irrelevant given that it was not accepted.