I don't think that you objects are changing really. If I have to guess, I should say that, maybe your properties used for map your objects only exist for IE, try to open a console in Chrome(F12 in Chrome) or Firefox and inspect your application's elements that fail to be recognized and see if they got there the properties used for your name mapping.
If you can't find them, then we can assume that those properties used for mapping are generated by IE (just like in Win objects ControlID and WndClass are generated automaticaly).
If that's not the case then, sorry but I don't know much than this,
EDIT: I didn't think about it but, do you wait for all your elements to be loaded before testing them ? If it's not the case, before testing an object do like this in your keyword test :
While...Loop(my.object.exist() == false )
{
delay(t)
}
Hope that can help you,
Nassim
