Every Firefox download has a unique identifier called dltoken

Next scandal, this is what people accused Chrome of when Chrome project started.

Chromes RLZ, that was killed after criticism.

dltoken is tied to telemetry.

There are apparently several unique IDs that you only can reset but not remove.

clearPref(“app.normandy.user_id”);
clearPref(“browser.newtabpage.activity-stream.impressionId”);
clearPref(“toolkit.telemetry.cachedClientID”);

Update

Someone correctly pointed out that linux downloads from the official homepage don't have the dltoken.