diff --git a/tools/serve/serve.py b/tools/serve/serve.py
index c4afc691d34d70..d920b841138172 100644
--- a/tools/serve/serve.py
+++ b/tools/serve/serve.py
@@ -16,6 +16,7 @@
 from six.moves import urllib
 import uuid
 from collections import defaultdict, OrderedDict
+from itertools import chain, product
 from multiprocessing import Process, Event
 
 from localpaths import repo_root
@@ -720,6 +721,9 @@ def build_config(override_path=None, **kwargs):
 
     return rv
 
+def _make_subdomains_product(s, depth=2):
+    return set(u".".join(x) for x in chain(*(product(s, repeat=i) for i in range(1, depth+1))))
+
 _subdomains = {u"www",
                u"www1",
                u"www2",
@@ -728,6 +732,10 @@ def build_config(override_path=None, **kwargs):
 
 _not_subdomains = {u"nonexistent"}
 
+_subdomains = _make_subdomains_product(_subdomains)
+
+_not_subdomains = _make_subdomains_product(_not_subdomains)
+
 
 class ConfigBuilder(config.ConfigBuilder):
     """serve config
diff --git a/tools/serve/test_serve.py b/tools/serve/test_serve.py
index 1c089b506738ee..62a6e74f980427 100644
--- a/tools/serve/test_serve.py
+++ b/tools/serve/test_serve.py
@@ -1,6 +1,7 @@
+import json
+import os
 import pickle
 import platform
-import os
 
 import pytest
 
@@ -75,3 +76,11 @@ def test_pickle():
     # Ensure that the config object can be pickled
     with ConfigBuilder() as c:
         pickle.dumps(c)
+
+
+def test_config_json_length():
+    # we serialize the config as JSON for pytestrunner and put it in an env
+    # variable, which on Windows must have a length <= 0x7FFF (int16)
+    with ConfigBuilder() as c:
+        data = json.dumps(c.as_dict())
+    assert len(data) <= 0x7FFF
diff --git a/tools/wptserve/tests/test_config.py b/tools/wptserve/tests/test_config.py
index 2ee8287710e91e..45f138f131d3bc 100644
--- a/tools/wptserve/tests/test_config.py
+++ b/tools/wptserve/tests/test_config.py
@@ -1,3 +1,4 @@
+import json
 import logging
 import pickle
 
@@ -43,6 +44,16 @@ def test_logger_preserved():
         assert c.logger is logger
 
 
+def test_as_dict():
+    with config.ConfigBuilder() as c:
+        assert c.as_dict() is not None
+
+
+def test_as_dict_is_json():
+    with config.ConfigBuilder() as c:
+        assert json.dumps(c.as_dict()) is not None
+
+
 def test_init_basic_prop():
     with config.ConfigBuilder(browser_host="foo.bar") as c:
         assert c.browser_host == "foo.bar"
diff --git a/tools/wptserve/wptserve/config.py b/tools/wptserve/wptserve/config.py
index cb5435fdef4c20..29c3d16b38e9a5 100644
--- a/tools/wptserve/wptserve/config.py
+++ b/tools/wptserve/wptserve/config.py
@@ -75,7 +75,9 @@ def json_types(obj):
         return {key: json_types(value) for key, value in iteritems(obj)}
     if (isinstance(obj, string_types) or
         isinstance(obj, integer_types) or
-        isinstance(obj, float)):
+        isinstance(obj, float) or
+        isinstance(obj, bool) or
+        obj is None):
         return obj
     if isinstance(obj, list) or hasattr(obj, "__iter__"):
         return [json_types(value) for value in obj]