I am currently experiencing a problem with the latest version of Firefox (5.0.1) and the Ancestry Enhanced Image Viewer. For some reason, Ancestry appear uninterested in upgrading their viewer and so it sometimes fails with versions 4 and 5 of Firefox!
If you have only recently started using Firefox, from version 4 or 5, then you probably never got the chance to use the Enhanced Image Viewer. All is not lost, however, as you can get it working. By downgrading Firefox!
Navigate to this page http://www.oldversion.com/Mozilla-Firefox.html and download one of the 3.5.x versions of Firefox. Make a note of where you save the file!
Close all Firefox Tabs and Windows and uninstall Firefox.
Install the 3.5.x version you downloaded earlier.
Navigate to an Ancestry census page – like this one for my great grandfather.
Ancestry should ask you to install the Enhanced Image Viewer and everything will be fine. If you have problems installing the Viewer go to this page and follow the instructions.
Once you have the viewer working you can upgrade your version of Firefox and it should stay working. If it doesn’t work after upgrading then go through the whole process again but install version 4 prior to upgrading to version 5.