go to
http://www.cb2.com/family.aspx?c=106&f=5377
try this expression: descendant::span[@class='breadcrumbSelected']
it doesn't work.
if you look at the code of the original page [not from firebug, it
corrects the error] you see they are using a single quote for the
class attribute insted of a double quote:
<span class='breadcrumbSelected'>
I hope it helps.
ciao