The comment by gruez is accurate IMO.

Creepjs actually tries to detect what your browser is lying about and takes that into consideration (or not) based on its heuristics.

I'm still not aware of any FOSS browser (with JS actually enabled and functioning) that can produce a random fingerprint ID on every refresh of the creepjs test site.

But please prove me wrong.

I've never heard of creepjs, are there more resources about it and where it's used?