Every once in a while — especially around the time of an upcoming new release — people argue that Firefox isn’t standards compliant, since it doesn’t score 100 on this test, but has been scoring 97 for quite a while, and will probably never implement what’s required to reach a score of 100.
via Alexander Limi – Mythbusting: Why Firefox 4 won’t score 100 on Acid3. Interesting stuff, though admittedly this is inside baseball stuff even for me.