Oh my, this is spectacularly to the point -

https://sinceyouarrived.world/taken

taken.

A web page that tells you what your browser gave away the moment you arrived. No login, no form, no permission. Most pages do this. None of them tell you.

Since You Arrived
@Natasha_Jay apparently my browser does well in protecting my privacy, because most of what I got was "[x] has been held back"
@iamada @Natasha_Jay Which browser are you using? 
@june @Natasha_Jay I'm using a somewhat hardened version of Zen, which is a fork of Firefox.
Zen Browser

Beautifully designed, privacy-focused, and packed with features.

@iamada @june @Natasha_Jay Hm, I think browsers should feed bogus data, just so sites wouldn't even detect it being held back. But it's not a trivial task, knowing the consequences of falling behind this treadmill: one data point slips out - and suddenly all users of the same browser pay the price.