He was fired for mentioning that Eisner and others at Disney were Jewish in his column. He was complaining about the fact that it was appalling to be releasing a movie like Kill Bill, with all its violence, considering the violence visited upon the Jewish people. A rather silly thing to say, but probably not worth firing him for it.
Mind you, he wrote this on his blog on TNR, rather than on ESPN.com.
Information on the controversy is found in his Wikipedia entry... http://en.wikipedia.org/wiki/Gregg_Easterbrook