https://check.torproject.org/?lang=en_US doesn't seem to check the
fingerprint very much. In fact, IceCat's fingerprint is different from Tor
Browser. With scripts enabled, it reports a different time zone than TBB, and
it reports your actual screen resolution whereas TBB reports the window size
(and sizes the window somewhat generically, always at a fixed width). With
scripts disabled, it's still not the same, because the two browsers have
slightly different values for HTTP_ACCEPT headers.
I checked with the EFF's tool:
https://panopticlick.eff.org/