new file mode 100644
--- /dev/null
+++ b/testing/config/Makefile.in
@@ -0,0 +1,24 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DEPTH = @DEPTH@
+topsrcdir = @top_srcdir@
+srcdir = @srcdir@
+VPATH = @srcdir@
+
+include $(DEPTH)/config/autoconf.mk
+include $(topsrcdir)/config/rules.mk
+
+CONFIG_FILES = \
+  mozharness_config.py \
+  $(NULL)
+
+_DEST_DIR = $(DEPTH)/_tests/config
+libs:: $(CONFIG_FILES)
+	$(PYTHON) $(topsrcdir)/config/nsinstall.py $^ $(_DEST_DIR)
+
+stage-package: PKG_STAGE = $(DIST)/test-package-stage
+stage-package:
+	$(NSINSTALL) -D $(PKG_STAGE)/config
+	@(cd $(srcdir) && tar $(TAR_CREATE_FLAGS) - $(CONFIG_FILES)) | (cd $(PKG_STAGE)/config && tar -xf -)

new file mode 100644
--- /dev/null
+++ b/testing/config/moz.build
@@ -0,0 +1,5 @@
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+

new file mode 100644
--- /dev/null
+++ b/testing/config/mozharness_config.py
@@ -0,0 +1,28 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+"""The config defined in this module is read by mozharness, which is a
+tool used to run many of the tests reporting to TBPL. This file is
+primarily useful for pushing custom test harness configurations to try.
+
+For example you can define a custom mochitest configuration by adding:
+    "mochitest_options": [
+        "--appname=%(binary_path)s", "--utility-path=tests/bin",
+        "--extra-profile-file=tests/bin/plugins", "--symbols-path=%(symbols_path)s",
+        "--certificate-path=tests/certs", "--autorun", "--close-when-done",
+        "--console-level=INFO", "--setpref=webgl.force-enabled=true"
+    ],
+
+Be warned that these values will be picked up by all platforms and changing them
+may result in unexpected behaviour. For example, the above will break B2G
+mochitests.
+
+You must also provide the complete command line to avoid errors. The official
+configuration files containing the default values live in:
+    https://hg.mozilla.org/build/mozharness/configs
+"""
+
+config = {
+    # Add custom mozharness config options here
+}

--- a/testing/testsuite-targets.mk
+++ b/testing/testsuite-targets.mk
@@ -383,16 +383,17 @@ pgo-profile-run:
 	$(PYTHON) $(DEPTH)/_profile/pgo/profileserver.py $(EXTRA_TEST_ARGS)
 
 # Package up the tests and test harnesses
 include $(topsrcdir)/toolkit/mozapps/installer/package-name.mk
 
 ifndef UNIVERSAL_BINARY
 PKG_STAGE = $(DIST)/test-package-stage
 package-tests: \
+  stage-config \
   stage-mochitest \
   stage-reftest \
   stage-xpcshell \
   stage-jstests \
   stage-jetpack \
   stage-peptest \
   stage-mozbase \
   stage-tps \
@@ -426,24 +427,28 @@ package-tests: stage-b2g
 endif
 
 make-stage-dir:
 	rm -rf $(PKG_STAGE)
 	$(NSINSTALL) -D $(PKG_STAGE)
 	$(NSINSTALL) -D $(PKG_STAGE)/bin
 	$(NSINSTALL) -D $(PKG_STAGE)/bin/components
 	$(NSINSTALL) -D $(PKG_STAGE)/certs
+	$(NSINSTALL) -D $(PKG_STAGE)/config
 	$(NSINSTALL) -D $(PKG_STAGE)/jetpack
 	$(NSINSTALL) -D $(PKG_STAGE)/peptest
 	$(NSINSTALL) -D $(PKG_STAGE)/mozbase
 	$(NSINSTALL) -D $(PKG_STAGE)/modules
 
 stage-b2g: make-stage-dir
 	$(NSINSTALL) $(topsrcdir)/b2g/test/b2g-unittest-requirements.txt $(PKG_STAGE)/b2g
 
+stage-config: make-stage-dir
+	$(MAKE) -C $(DEPTH)/testing/config stage-package
+
 stage-mochitest: make-stage-dir
 	$(MAKE) -C $(DEPTH)/testing/mochitest stage-package
 ifeq ($(MOZ_BUILD_APP),mobile/android)
 	$(NSINSTALL) $(DEPTH)/mobile/android/base/fennec_ids.txt $(PKG_STAGE)/mochitest
 endif
 
 stage-reftest: make-stage-dir
 	$(MAKE) -C $(DEPTH)/layout/tools/reftest stage-package
@@ -502,16 +507,17 @@ stage-mozbase: make-stage-dir
   reftest \
   crashtest \
   xpcshell-tests \
   jstestbrowser \
   peptest \
   package-tests \
   make-stage-dir \
   stage-b2g \
+  stage-config \
   stage-mochitest \
   stage-reftest \
   stage-xpcshell \
   stage-jstests \
   stage-android \
   stage-jetpack \
   stage-peptest \
   stage-mozbase \

--- a/toolkit/toolkit.mozbuild
+++ b/toolkit/toolkit.mozbuild
@@ -228,16 +228,17 @@ add_tier_dir('platform', 'addon-sdk')
 if CONFIG['MOZ_MAPINFO']:
     add_tier_dir('platform', 'tools/codesighs')
 
 if CONFIG['ENABLE_MARIONETTE']:
     add_tier_dir('platform', 'testing/marionette')
 
 if CONFIG['ENABLE_TESTS']:
     add_tier_dir('platform', [
+        'testing/config',
         'testing/mochitest',
         'testing/xpcshell',
         'testing/tools/screenshot',
         'testing/peptest',
         'testing/profiles',
         'testing/mozbase',
         'testing/modules',
     ])