If it starts including things like display size, device, etc. then you get into the realm of browser fingerprinting which while maybe not truly unique does star

If it starts including things like display size, device, etc. then you get into the realm of browser fingerprinting which while maybe not truly unique does start to narrow the pool quite a bit: https://panopticlick.eff.org/about#browser-fingerprinting https://panopticlick.eff.org/about#browser-fingerprinting