--- a/testing/marionette/harness/marionette/__init__.py
+++ b/testing/marionette/harness/marionette/__init__.py
@@ -6,16 +6,17 @@
 
 from .marionette_test import (
     CommonTestCase,
     expectedFailure,
     MarionetteJSTestCase,
     MarionetteTestCase,
     skip,
     skip_if_desktop,
+    skip_if_mobile,
     SkipTest,
     skip_unless_protocol,
 )
 from .runner import (
     BaseMarionetteArguments,
     BaseMarionetteTestRunner,
     BrowserMobProxyTestCaseMixin,
     EnduranceArguments,

--- a/testing/marionette/harness/marionette/marionette_test.py
+++ b/testing/marionette/harness/marionette/marionette_test.py
@@ -83,21 +83,28 @@ def skip_if_chrome(target):
     def wrapper(self, *args, **kwargs):
         if self.marionette._send_message("getContext", key="value") == "chrome":
             raise SkipTest("skipping test in chrome context")
         return target(self, *args, **kwargs)
     return wrapper
 
 def skip_if_desktop(target):
     def wrapper(self, *args, **kwargs):
-        if self.marionette.session_capabilities.get('b2g') is None:
+        if self.marionette.session_capabilities.get('browserName') == 'firefox':
             raise SkipTest('skipping due to desktop')
         return target(self, *args, **kwargs)
     return wrapper
 
+def skip_if_mobile(target):
+    def wrapper(self, *args, **kwargs):
+        if self.marionette.session_capabilities.get('browserName') == 'fennec':
+            raise SkipTest('skipping due to fennec')
+        return target(self, *args, **kwargs)
+    return wrapper
+
 def skip_if_e10s(target):
     def wrapper(self, *args, **kwargs):
         with self.marionette.using_context('chrome'):
             multi_process_browser = self.marionette.execute_script("""
             try {
               return Services.appinfo.browserTabsRemoteAutostart;
             } catch (e) {
               return false;