diff --git a/gfx/wr/wrench/android.txt b/gfx/wr/wrench/android.txt
index c51985b712eb..f0f428809e70 100644
--- a/gfx/wr/wrench/android.txt
+++ b/gfx/wr/wrench/android.txt
@@ -59,8 +59,8 @@ Release mode:
     should be signed and installable (you may need to uninstall the debug APK first if you
     have that installed).
 
-Running reftests like a boss:
------------------------------
+Running reftests like a boss (on a local emulator):
+---------------------------------------------------
 
     First, compile wrench as described above (debug mode).
     Then, from the root gecko source dir, run:
@@ -84,3 +84,13 @@ Running reftests like a boss:
     to point to it:
         export WRENCH_APK=gfx/wr/target/android-artifacts/app/build/outputs/apk/app-release-unsigned.apk
         ./mach python testing/mozharness/scripts/android_wrench.py --config testing/mozharness/configs/android/wrench.py
+
+Running reftests like a boss (on a local device):
+-------------------------------------------------
+
+    Same steps as running on a local emulator, except you need to do this:
+        export DEVICE_SERIAL=<your device's serial>
+    before running the `./mach python` command. You can get the serial of
+    your device by running `adb devices` with the device plugged in. When running
+    on a device, the android_emulator_wrench.py script will skip the steps to
+    download the AVDs and start the emulator.
diff --git a/testing/mozharness/configs/android/wrench.py b/testing/mozharness/configs/android/wrench.py
index 48c20596b02e..8299f6aa8250 100644
--- a/testing/mozharness/configs/android/wrench.py
+++ b/testing/mozharness/configs/android/wrench.py
@@ -20,7 +20,6 @@ config = {
     "emulator_process_name": "emulator64-x86",
     "emulator_extra_args": "-gpu swiftshader_indirect -skip-adb-auth -verbose -show-kernel -use-system-libs -ranchu -selinux permissive -memory 3072 -cores 4",
     "exes": {
-        'adb': '%(abs_work_dir)s/android-sdk-linux/platform-tools/adb',
     },
     "env": {
         "DISPLAY": ":0.0",
diff --git a/testing/mozharness/scripts/android_wrench.py b/testing/mozharness/scripts/android_wrench.py
index c89201ffe56c..1e3eae4053a3 100644
--- a/testing/mozharness/scripts/android_wrench.py
+++ b/testing/mozharness/scripts/android_wrench.py
@@ -26,11 +26,37 @@ from mozharness.mozilla.testing.testbase import TestingMixin
 
 class AndroidWrench(TestingMixin, BaseScript, MozbaseMixin, AndroidMixin):
     def __init__(self, require_config_file=False):
+        # code in BaseScript.__init__ iterates all the properties to attach
+        # pre- and post-flight listeners, so we need _is_emulator be defined
+        # before that happens. Doesn't need to be a real value though.
+        self._is_emulator = None
+
         super(AndroidWrench, self).__init__()
-        self.device_serial = 'emulator-5554'
-        self.use_gles3 = True
+        if self.device_serial is None:
+            # Running on an emulator. Need absolute path to adb
+            # to satisfy android.py's start_emulator function.
+            self._is_emulator = True
+            self.device_serial = 'emulator-5554'
+            self._adb_path = os.path.join(
+                self.query_abs_dirs()['abs_work_dir'],
+                'android-sdk-linux',
+                'platform-tools',
+                'adb')
+            self.use_gles3 = True
+        else:
+            # Running on a device, ensure self.is_emulator returns False.
+            # Also don't set the adb path explicitly, since it should be
+            # on the $PATH anyway and we don't have an easy way to get the
+            # absolute path in automation (it's preinstalled on the bitbar
+            # image).
+            self._is_emulator = False
         self._errored = False
 
+    @property
+    def is_emulator(self):
+        """Overrides the is_emulator property on AndroidMixin."""
+        return self._is_emulator
+
     def query_abs_dirs(self):
         if self.abs_dirs:
             return self.abs_dirs
@@ -96,7 +122,10 @@ class AndroidWrench(TestingMixin, BaseScript, MozbaseMixin, AndroidMixin):
         args_file = os.path.join(
             self.query_abs_dirs()['abs_work_dir'], "wrench_args")
         with open(args_file, 'w') as argfile:
-            argfile.write("env: WRENCH_REFTEST_CONDITION_EMULATOR=1\n")
+            if self.is_emulator:
+                argfile.write("env: WRENCH_REFTEST_CONDITION_EMULATOR=1\n")
+            else:
+                argfile.write("env: WRENCH_REFTEST_CONDITION_DEVICE=1\n")
             argfile.write("reftest")
         self.device.push(args_file, '/sdcard/wrench/args')
 
@@ -158,7 +187,7 @@ class AndroidWrench(TestingMixin, BaseScript, MozbaseMixin, AndroidMixin):
             self.info("=== end scraped logcat output ===")
             self.info("(see logcat artifact for full logcat")
 
-    def do_test(self):
+    def setup_emulator(self):
         # Running setup_avds will clobber the existing AVD and redownload it.
         # For local testing that's kinda expensive, so we omit that if we
         # already have that dir.
@@ -188,8 +217,11 @@ class AndroidWrench(TestingMixin, BaseScript, MozbaseMixin, AndroidMixin):
                     return
             self._launch_emulator()
 
-        self.verify_device()
+    def do_test(self):
+        if self.is_emulator:
+            self.setup_emulator()
 
+        self.verify_device()
         self.info('Installing APK...')
         self.install_apk(self.query_abs_dirs()['abs_apk_path'], replace=True)
         self.info('Setting up SD card...')