No amount of tweeking will make IE8 work properly on Ancestry - apparently.
Sorry, but that's just not true !
I have been using IE8 since the Beta 2 version, and the only thing that didn't work properly in Ancestry was the editing of profiles (which used a Java script which didn't run properly on IE8), but this was more of an annoyance, because it would work if you persisted. This has now been fixed by Ancestry.
There were also a few page presentation issues, which made the pages look a little odd sometimes, but these were fixed by running in compatability mode. These issues have also now been completely fixed.
I have tried to use Firefox on Ancestry, but always found that pages looked worse than they did in IE, especially the timeline in the profile view. I also could not find a way to make the Ancestry enhanced image viewer work, and I did try very hard to make it work.
Now I can honestly say that I have no issues with IE8 and Ancestry, even with the compatability mode off. I think this may be as a result of millions of Americans switching to IE8, and complaining about the issues they had. Ancestry didn't want to know when I was Beta testing, although I did try to warn them that IE8 would be a popular browser within a few months.