What does that mean? I keep getting 71 
Something is crippling Firefox's ability to handle Javascript, Document Object Modeling, and other Web standards (zooming, disabling images, add-ons, etc.). The more that the browser successfully renders (or completes), the higher the score will be.
You can get more information of what your Firefox failed by clicking the "A".
http://acid2.acidtests.org/#top would be a better test to diagnose a possible problem with why that happens but unfortunately there isn't a pass/fail report. If it is distorted or you see any red, the test failed (which should never happen with most modern browsers without interference).
Edited by Kweh, 04 January 2010 - 10:05 AM.