The problem seems to be with the dnn.dom.positioning.js file.
on line 246 the js code states :-
var iIndex = dnn.dom.getCurrentStyle(oCont, 'zIndex');
if (iIndex == null || iIndex == 0)
oCont.style.zIndex = 1;
oIFR.style.zIndex=iIndex-1;
oIFR.style.display="block";
as iIndex can contain the value "auto", subtracting 1 from it causes IE to stop the js execution whereas FF will continue
To solve the problem I changed this to
var iIndex = dnn.dom.getCurrentStyle(oCont, 'zIndex');
if (iIndex == null || iIndex == 0)
oCont.style.zIndex = 1;
if (iIndex == 'auto')
{
oIFR.style.zIndex=1;
}
else
{
oIFR.style.zIndex=iIndex-1;
}
oIFR.style.display="block";
although someone else may want to come up with a more elegant solution than simply making iIndex 1 when it has been set to auto ?