--- a/testing/web-platform/mach_commands.py
+++ b/testing/web-platform/mach_commands.py
@@ -68,58 +68,49 @@ class WebPlatformTestsRunnerSetup(Mozbui
 
         if kwargs["webdriver_binary"] is None:
             kwargs["webdriver_binary"] = self.get_binary_path("geckodriver", validate_exists=False)
 
         self.setup_fonts_firefox()
 
         kwargs = wptcommandline.check_args(kwargs)
 
+        return kwargs
+
     def kwargs_wptrun(self, kwargs):
         from wptrunner import wptcommandline
         here = os.path.join(self.topsrcdir, 'testing', 'web-platform')
 
-        sys.path.insert(0, os.path.join(here, "tests", "tools"))
-
-        import wptrun
-
-        product = kwargs["product"]
-
-        setup_func = {
-            "chrome": wptrun.setup_chrome,
-            "edge": wptrun.setup_edge,
-            "servo": wptrun.setup_servo,
-        }[product]
+        kwargs["tests_root"] = os.path.join(here, "tests")
 
-        try:
-            wptrun.check_environ(product)
-
-            setup_func(wptrun.virtualenv.Virtualenv(self.virtualenv_manager.virtualenv_root),
-                       kwargs,
-                       True)
-        except wptrun.WptrunError as e:
-            print(e.message, file=sys.stderr)
-            sys.exit(1)
-
-        kwargs["tests_root"] = os.path.join(here, "tests")
+        sys.path.insert(0, kwargs["tests_root"])
 
         if kwargs["metadata_root"] is None:
             metadir = os.path.join(here, "products", kwargs["product"])
             if not os.path.exists(metadir):
                 os.makedirs(metadir)
             kwargs["metadata_root"] = metadir
 
         src_manifest = os.path.join(here, "meta", "MANIFEST.json")
         dest_manifest = os.path.join(kwargs["metadata_root"], "MANIFEST.json")
 
         if not os.path.exists(dest_manifest) and os.path.exists(src_manifest):
             with open(src_manifest) as src, open(dest_manifest, "w") as dest:
                 dest.write(src.read())
 
-        kwargs = wptcommandline.check_args(kwargs)
+        from tools.wpt import run
+
+        try:
+            kwargs = run.setup_wptrunner(run.virtualenv.Virtualenv(self.virtualenv_manager.virtualenv_root),
+                                         **kwargs)
+        except run.WptrunError as e:
+            print(e.message, file=sys.stderr)
+            sys.exit(1)
+
+        return kwargs
 
     def setup_fonts_firefox(self):
         # Ensure the Ahem font is available
         if not sys.platform.startswith("darwin"):
             font_path = os.path.join(os.path.dirname(self.get_binary_path()), "fonts")
         else:
             font_path = os.path.join(os.path.dirname(self.get_binary_path()), os.pardir, "Resources", "res", "fonts")
         ahem_src = os.path.join(self.topsrcdir, "testing", "web-platform", "tests", "fonts", "Ahem.ttf")

--- a/testing/web-platform/mach_commands_base.py
+++ b/testing/web-platform/mach_commands_base.py
@@ -14,16 +14,16 @@ class WebPlatformTestsRunner(object):
     """Run web platform tests."""
 
     def __init__(self, setup):
         self.setup = setup
 
     def run(self, **kwargs):
         from wptrunner import wptrunner
         if kwargs["product"] in ["firefox", None]:
-            self.setup.kwargs_firefox(kwargs)
+            kwargs = self.setup.kwargs_firefox(kwargs)
         elif kwargs["product"] in ("chrome", "edge", "servo"):
-            self.setup.kwargs_wptrun(kwargs)
+            kwargs = self.setup.kwargs_wptrun(kwargs)
         else:
             raise ValueError("Unknown product %s" % kwargs["product"])
         logger = wptrunner.setup_logging(kwargs, {self.setup.default_log_type: sys.stdout})
         result = wptrunner.start(**kwargs)
         return int(not result)