Comment by drnick1

> If you put too much in your Telemetry/crash reports, yeah, users become fingerprintable.

It's not only what gets send to Mozilla as telemetry or crash reports that is a problem. That can be turned off (many Linux distros do), or firewalled.

The main issue is that websites can more or less accurately identify users uniquely by extracting information that they should not have access to if the browser was designed with privacy in mind.

This includes, but is not limited to, fonts installed, system language, time zone, window size, browser version, hardware information (number of cores, device memory), canvas fingerprint, and many others attributes. When you combine all of that with the originating IP address, you can reliably determine who visited a website, because that information is shared and correlated with services where people identify themselves (Google accounts, Facebook, Amazon, etc.) Even masking your IP may not be enough because typically there is enough information in the other data points to track you already.