py: Fixing Firefox extension ID extraction.

Some extensions (e.g foxyproxy) declare rdf namespace twice -- as a
named namespace and as a default one. So we have to make two attempts to
read this section.

Author: barancev

Diff for: py/selenium/webdriver/firefox/firefox_profile.py

@@ -356,6 +356,8 @@ def get_text(element):
             rdf = get_namespace_id(doc, 'http://www.w3.org/1999/02/22-rdf-syntax-ns#')
 
             description = doc.getElementsByTagName(rdf + 'Description').item(0)
+            if description is None:
+                description = doc.getElementsByTagName('Description').item(0)
             for node in description.childNodes:
                 # Remove the namespace prefix from the tag for comparison
                 entry = node.nodeName.replace(em, "")