NW.js fullscreen mode is actually borderless windowed, not true fullscreen

Question

I'm working on a game using NW.js, one that I'd like to be fullscreen. The fullscreen mode does in fact make the game fullscreen, but it's not true fullscreen like many other games, it's borderless windowed.

This is affecting performance for other players, so I'm trying my best to get true fullscreen. Is this not possible with NW.js, or even anything Chromium?

My NW.js manifest:

"window": {
  "title": "Slapshot",
  "frame": false,
  "width": 800,
  "height": 600,
  "icon": "assets/textures/icon.png",
  "fullscreen": true,
  "toolbar": false
},