Sorry for the unclear response. EDNS0 is what we call the DNS extensions that were added via RFC 2671. In the past, the PIX enforced a 512 byte limit to DNS queries but as of this RFC, it is now valid to have DNS queries that exceed this limit. So, we added a new fixup to the PIX to support this change. See the following from the release notes:
http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_sw/v_63/63rnotes/pixrn632.htm#110415
Scott
