See also the article [Why there are so many Debian derivatives](http://upsilon.cc/~zack/blog/posts/2011/09/why_there_are_so_many_debian_derivatives/)by Stefano Zacchiroli.
So, the information retrieved by such fingerprinting websites is not harmful for anonymity in itself, as long as it is the same for all users of *Tor Browser*.
For example, the user-agent string of *Tor Browser* includes <em>Windows NT</em> but this value preserves your anonymity even if you run Windows NT. On the other hand, changing this value makes you distinguishable from other users of *Tor Browser* and, as a consequence, weakens your anonymity.