I don’t mean this in the way treated at https://panopticlick.eff.org/
but specifically I just got an e-mail when signing up for discourse that said:
Click and confirm that you want to sign in to discourse.mozilla-community.org. Please sign in using the same web browser that you used to generate this link. The link will expire in five minutes.
Why do I need to use the same browser and how can you tell?