--- a/testing/mozharness/scripts/web_platform_tests.py
+++ b/testing/mozharness/scripts/web_platform_tests.py
@@ -237,16 +237,17 @@ class WebPlatformTest(TestingMixin, Merc
                     cmd.append("--%s=%s" % (opt.replace("_", "-"), val))
 
         if "wdspec" in test_types:
             geckodriver_path = self._query_geckodriver()
             if not geckodriver_path or not os.path.isfile(geckodriver_path):
                 self.fatal("Unable to find geckodriver binary "
                            "in common test package: %s" % str(geckodriver_path))
             cmd.append("--webdriver-binary=%s" % geckodriver_path)
+            cmd.append("--webdriver-arg=-vv")  # enable trace logs
 
         options = list(c.get("options", []))
 
         str_format_values = {
             'binary_path': self.binary_path,
             'test_path': dirs["abs_wpttest_dir"],
             'test_install_path': dirs["abs_test_install_dir"],
             'abs_app_dir': abs_app_dir,