--- a/testing/marionette/harness/marionette_harness/runner/base.py
+++ b/testing/marionette/harness/marionette_harness/runner/base.py
@@ -356,21 +356,21 @@ class BaseMarionetteArguments(ArgumentPa
                           default=self.socket_timeout_default,
                           help='Set the global timeout for marionette socket operations.'
                                ' Default: %(default)ss.')
         self.add_argument('--disable-e10s',
                           action='store_false',
                           dest='e10s',
                           default=True,
                           help='Disable e10s when running marionette tests.')
-        self.add_argument('--headless',
-                          action='store_true',
-                          dest='headless',
-                          default=False,
-                          help='Enable headless mode when running marionette tests.')
+        self.add_argument("--headless",
+                          action="store_true",
+                          dest="headless",
+                          default=os.environ.get("MOZ_HEADLESS", False),
+                          help="Run tests in headless mode.")
         self.add_argument('--tag',
                           action='append', dest='test_tags',
                           default=None,
                           help="Filter out tests that don't have the given tag. Can be "
                                "used multiple times in which case the test must contain "
                                "at least one of the given tags.")
         self.add_argument('--workspace',
                           action='store',