Bug / design issue in Firefox that allows precise tracking of individual users?

Firefox Development
#1

Please take a look at this discussion. If this is true, there must be a massive bug in Firefox that allows precise tracking of individual users despite deleting all browser history!

#2

Keep track on https://bugzilla.mozilla.org/show_bug.cgi?id=1400582.

This may be https://bugzilla.mozilla.org/show_bug.cgi?id=1047098.