diff --git a/apps/amo/__init__.py b/apps/amo/__init__.py
index 9b2d5f90db..89e39b7452 100644
--- a/apps/amo/__init__.py
+++ b/apps/amo/__init__.py
@@ -222,6 +222,8 @@ class MOZILLA:
              ADDON_LPAPP, ADDON_PLUGIN]
     guid = '{86c18b42-e466-45a9-ae7a-9b95ba6f5640}'
 
+# UAs will attempt to match in this order
+APP_DETECT = (MOBILE, FIREFOX, THUNDERBIRD, SEAMONKEY, SUNBIRD)
 APP_USAGE = _apps = (FIREFOX, THUNDERBIRD, MOBILE, SEAMONKEY, SUNBIRD)
 APPS = dict((app.short, app) for app in _apps)
 APP_IDS = dict((app.id, app) for app in _apps)
diff --git a/apps/amo/tests/test_url_prefix.py b/apps/amo/tests/test_url_prefix.py
index 60e28c7253..48f2b93b76 100644
--- a/apps/amo/tests/test_url_prefix.py
+++ b/apps/amo/tests/test_url_prefix.py
@@ -72,6 +72,9 @@ class MiddlewareTest(test.TestCase):
         check('/en-US/', '/en-US/firefox/', 'Firefox')
         check('/de/', '/de/mobile/', 'Fennec')
 
+        # Mobile gets priority because it has both strings in its UA...
+        check('/de/', '/de/mobile/', 'Firefox Fennec')
+
     def test_get_lang(self):
         def check(url, expected):
             response = self.process(url)
diff --git a/apps/amo/urlresolvers.py b/apps/amo/urlresolvers.py
index 9c15d5b652..eb2d693db8 100644
--- a/apps/amo/urlresolvers.py
+++ b/apps/amo/urlresolvers.py
@@ -100,14 +100,13 @@ class Prefixer(object):
         Return a valid application string using the User Agent to guess.  Falls
         back to settings.DEFAULT_APP.
         """
-        app = settings.DEFAULT_APP
         ua = self.request.META.get('HTTP_USER_AGENT')
         if ua:
-            for i in amo.APPS.values():
-                if i.user_agent_string in ua:
-                    app = i.short
+            for app in amo.APP_DETECT:
+                if app.user_agent_string in ua:
+                    return app.short
 
-        return app
+        return settings.DEFAULT_APP
 
     def get_language(self):
         """