--- a/testing/web-platform/tests/webdriver/tests/support/fixtures.py
+++ b/testing/web-platform/tests/webdriver/tests/support/fixtures.py
@@ -208,16 +208,17 @@ def new_session(configuration, request):
         global _current_session
         _session = webdriver.Session(configuration["host"],
                                      configuration["port"],
                                      capabilities=None)
         value = _session.send_command("POST", "session", body=body)
         # Don't set the global session until we are sure this succeeded
         _current_session = _session
         _session.session_id = value["sessionId"]
+        _session.capabilities = value["capabilities"]
 
         return value, _current_session
 
     end()
 
     # finalisers are popped off a stack, making their ordering reverse
     request.addfinalizer(end)
     request.addfinalizer(_switch_to_top_level_browsing_context)