--- a/testing/mozharness/configs/marionette/prod_config.py
+++ b/testing/mozharness/configs/marionette/prod_config.py
@@ -26,31 +26,31 @@ config = {
         'clobber',
         'read-buildbot-config',
         'download-and-extract',
         'create-virtualenv',
         'install',
         'run-tests',
     ],
     "default_blob_upload_servers": [
-         "https://blobupload.elasticbeanstalk.com",
+        "https://blobupload.elasticbeanstalk.com",
     ],
-    "blob_uploader_auth_file" : os.path.join(os.getcwd(), "oauth.txt"),
+    "blob_uploader_auth_file": os.path.join(os.getcwd(), "oauth.txt"),
     "download_symbols": "ondemand",
     "download_minidump_stackwalk": True,
     "tooltool_cache": "/builds/worker/tooltool-cache",
     "suite_definitions": {
         "marionette_desktop": {
             "options": [
                 "-vv",
                 "--log-raw=%(raw_log_file)s",
                 "--log-errorsummary=%(error_summary_file)s",
                 "--log-html=%(html_report_file)s",
                 "--binary=%(binary)s",
                 "--address=%(address)s",
                 "--symbols-path=%(symbols_path)s"
             ],
             "run_filename": "",
-            "testsdir": ""
+            "testsdir": "marionette"
         }
     },
     "structured_output": True,
 }

--- a/testing/mozharness/configs/marionette/test_config.py
+++ b/testing/mozharness/configs/marionette/test_config.py
@@ -19,12 +19,12 @@ config = {
                 "--log-raw=%(raw_log_file)s",
                 "--log-errorsummary=%(error_summary_file)s",
                 "--log-html=%(html_report_file)s",
                 "--binary=%(binary)s",
                 "--address=%(address)s",
                 "--symbols-path=%(symbols_path)s"
             ],
             "run_filename": "",
-            "testsdir": ""
+            "testsdir": "marionette"
         },
     },
 }

--- a/testing/mozharness/configs/marionette/windows_config.py
+++ b/testing/mozharness/configs/marionette/windows_config.py
@@ -30,29 +30,29 @@ config = {
         'clobber',
         'read-buildbot-config',
         'download-and-extract',
         'create-virtualenv',
         'install',
         'run-tests',
     ],
     "default_blob_upload_servers": [
-         "https://blobupload.elasticbeanstalk.com",
+        "https://blobupload.elasticbeanstalk.com",
     ],
-    "blob_uploader_auth_file" : os.path.join(os.getcwd(), "oauth.txt"),
+    "blob_uploader_auth_file": os.path.join(os.getcwd(), "oauth.txt"),
     "download_minidump_stackwalk": True,
     "download_symbols": "ondemand",
     "suite_definitions": {
         "marionette_desktop": {
             "options": [
                 "-vv",
                 "--log-raw=%(raw_log_file)s",
                 "--log-errorsummary=%(error_summary_file)s",
                 "--log-html=%(html_report_file)s",
                 "--binary=%(binary)s",
                 "--address=%(address)s",
                 "--symbols-path=%(symbols_path)s"
             ],
             "run_filename": "",
-            "testsdir": ""
+            "testsdir": "marionette"
         },
     },
 }

--- a/testing/mozharness/configs/marionette/windows_taskcluster_config.py
+++ b/testing/mozharness/configs/marionette/windows_taskcluster_config.py
@@ -29,29 +29,29 @@ config = {
     "default_actions": [
         'clobber',
         'download-and-extract',
         'create-virtualenv',
         'install',
         'run-tests',
     ],
     "default_blob_upload_servers": [
-         "https://blobupload.elasticbeanstalk.com",
+        "https://blobupload.elasticbeanstalk.com",
     ],
-    "blob_uploader_auth_file" : 'C:/builds/oauth.txt',
+    "blob_uploader_auth_file": 'C:/builds/oauth.txt',
     "download_minidump_stackwalk": True,
     "download_symbols": "ondemand",
     "suite_definitions": {
         "marionette_desktop": {
             "options": [
                 "-vv",
                 "--log-raw=%(raw_log_file)s",
                 "--log-errorsummary=%(error_summary_file)s",
                 "--log-html=%(html_report_file)s",
                 "--binary=%(binary)s",
                 "--address=%(address)s",
                 "--symbols-path=%(symbols_path)s"
             ],
             "run_filename": "",
-            "testsdir": ""
+            "testsdir": "marionette"
         },
     },
 }

--- a/testing/mozharness/scripts/marionette.py
+++ b/testing/mozharness/scripts/marionette.py
@@ -142,27 +142,37 @@ class MarionetteTest(TestingMixin, Mercu
         # these are necessary since self.config is read only
         c = self.config
         self.installer_url = c.get('installer_url')
         self.installer_path = c.get('installer_path')
         self.binary_path = c.get('binary_path')
         self.test_url = c.get('test_url')
         self.test_packages_url = c.get('test_packages_url')
 
+        self.test_suite = self._get_test_suite(c.get('emulator'))
+        if self.test_suite not in self.config["suite_definitions"]:
+            self.fatal("{} is not defined in the config!".format(self.test_suite))
+
         if c.get('structured_output'):
             self.parser_class = StructuredOutputParser
         else:
             self.parser_class = TestSummaryOutputParserHelper
 
     def _pre_config_lock(self, rw_config):
         super(MarionetteTest, self)._pre_config_lock(rw_config)
         if not self.config.get('emulator') and not self.config.get('marionette_address'):
                 self.fatal("You need to specify a --marionette-address for non-emulator tests! "
                            "(Try --marionette-address localhost:2828 )")
 
+    def _query_tests_dir(self):
+        dirs = self.query_abs_dirs()
+        test_dir = self.config["suite_definitions"][self.test_suite]["testsdir"]
+
+        return os.path.join(dirs['abs_test_install_dir'], test_dir)
+
     def query_abs_dirs(self):
         if self.abs_dirs:
             return self.abs_dirs
         abs_dirs = super(MarionetteTest, self).query_abs_dirs()
         dirs = {}
         dirs['abs_test_install_dir'] = os.path.join(
             abs_dirs['abs_work_dir'], 'tests')
         dirs['abs_marionette_dir'] = os.path.join(
@@ -204,17 +214,17 @@ class MarionetteTest(TestingMixin, Mercu
                       'mozcrash', 'mozinstall', 'mozdevice', 'mozprofile',
                       'mozprocess', 'mozrunner'):
                 self.register_virtualenv_module(
                     m, os.path.join(mozbase_dir, m))
 
             self.register_virtualenv_module(
                 'marionette', os.path.join('tests', 'marionette'))
 
-    def _get_options_group(self, is_emulator):
+    def _get_test_suite(self, is_emulator):
         """
         Determine which in tree options group to use and return the
         appropriate key.
         """
         platform = 'emulator' if is_emulator else 'desktop'
         # Currently running marionette on an emulator means webapi
         # tests. This method will need to change if this does.
         testsuite = 'webapi' if is_emulator else 'marionette'
@@ -290,23 +300,18 @@ class MarionetteTest(TestingMixin, Mercu
         if self.config['headless']:
             cmd.append('--headless')
 
         cmd.append('--gecko-log=-')
 
         if self.config.get("structured_output"):
             cmd.append("--log-raw=-")
 
-        options_group = self._get_options_group(self.config.get('emulator'))
-
-        if options_group not in self.config["suite_definitions"]:
-            self.fatal("%s is not defined in the config!" % options_group)
-
-        for s in self.config["suite_definitions"][options_group]["options"]:
-            cmd.append(s % config_fmt_args)
+        for arg in self.config["suite_definitions"][self.test_suite]["options"]:
+            cmd.append(arg % config_fmt_args)
 
         if self.mkdir_p(dirs["abs_blob_upload_dir"]) == -1:
             # Make sure that the logging directory exists
             self.fatal("Could not create blobber upload directory")
 
         cmd.append(manifest)
 
         try_options, try_tests = self.try_args("marionette")
@@ -325,21 +330,28 @@ class MarionetteTest(TestingMixin, Mercu
         if self.config['enable_webrender']:
             env['MOZ_WEBRENDER'] = '1'
             env['MOZ_ACCELERATED'] = '1'
 
         if not os.path.isdir(env['MOZ_UPLOAD_DIR']):
             self.mkdir_p(env['MOZ_UPLOAD_DIR'])
         env = self.query_env(partial_env=env)
 
+        try:
+            cwd = self._query_tests_dir()
+        except Exception as e:
+            self.fatal("Don't know how to run --test-suite '{0}': {1}!".format(
+                self.test_suite, e))
+
         marionette_parser = self.parser_class(config=self.config,
                                               log_obj=self.log_obj,
                                               error_list=BaseErrorList + HarnessErrorList,
                                               strict=False)
         return_code = self.run_command(cmd,
+                                       cwd=cwd,
                                        output_timeout=1000,
                                        output_parser=marionette_parser,
                                        env=env)
         level = INFO
         tbpl_status, log_level = marionette_parser.evaluate_parser(
             return_code=return_code)
         marionette_parser.append_tinderboxprint_line("marionette")