TVbytheNumbers has published final Nielsen ratings for Sunday and "FOX's 25th Anniversary Special" averaged just 4.32 million viewers and a 1.8/5 A18-49 rating from 8-10PM. It ranked fourth in viewers but third in the demo, beating Harry's Law on NBC from 8-9PM and the first half of the latest Hallmark Hall of Fame telefilm, Firelight, on ABC from 9-10PM. Those are pretty sad numbers no matter how you look at them, particularly given the promotion FOX seems to have put behind the special. By comparison, "ABC's 50th Anniversary Celebration" (broadcast in May of 2003) was seen by 11.4 million viewers and "CBS at 75" (broadcast in November of 2003), drew more than 18 million viewers and a 3.9/10 A18-49 rating.
Confession: I recorded but did not watch "FOX's 25th Anniversary Special" on Sunday.