Hello,
This is going to change sometime next week when we release a Firefox version. In the meantime if you want to get your page tested, I recommend just copying the following function out of our Javascript example and using it. Unfortunately you can't call ours directly because it is buried in the hdvHost object. We should probably change our javascript so that you can just call this directly. Also the script snippet below is IE specific.
function isHDViewInstalled()
{
var installed = false;
try
{
var hdvCntrl = new ActiveXObject("Viewer.ViewCtl");
installed = true;
}
catch (e) {}
return installed;
}