--- a/build/virtualenv_packages.txt
+++ b/build/virtualenv_packages.txt
@@ -1,2 +1,1 @@
 comm.pth:comm/taskcluster
-comm.pth:comm/testing/marionette

deleted file mode 100644
--- a/mail/test/marionette/manifest.ini
+++ /dev/null
@@ -1,1 +0,0 @@
-[test_empty.py]

deleted file mode 100644
--- a/mail/test/marionette/moz.build
+++ /dev/null
@@ -1,6 +0,0 @@
-# vim: set filetype=python:
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at http://mozilla.org/MPL/2.0/.
-
-MARIONETTE_UNIT_MANIFESTS += ['manifest.ini']

deleted file mode 100644
--- a/mail/test/marionette/test_empty.py
+++ /dev/null
@@ -1,12 +0,0 @@
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at http://mozilla.org/MPL/2.0/.
-
-from __future__ import print_function
-
-from marionette_harness import MarionetteTestCase
-
-class TestMain(MarionetteTestCase):
-
-    def test_empty(self):
-        return

--- a/taskcluster/ci/test/kind.yml
+++ b/taskcluster/ci/test/kind.yml
@@ -13,9 +13,8 @@ kind-dependencies:
 transforms:
     - taskgraph.transforms.tests:transforms
     - comm_taskgraph:tests_drop_1proc
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 jobs-from:
     - tests.yml
-    - marionette.yml

deleted file mode 100644
--- a/taskcluster/ci/test/marionette.yml
+++ /dev/null
@@ -1,36 +0,0 @@
-job-defaults:
-    suite: marionette
-    mozharness:
-        script: marionette.py
-        config:
-            by-test-platform:
-                macosx.*:
-                    - marionette/prod_config.py
-                    - marionette/mac_taskcluster_config.py
-                windows.*:
-                    - marionette/windows_taskcluster_config.py
-                default:
-                    - marionette/prod_config.py
-                    - remove_executables.py
-        extra-options:
-            - --application=thunderbird --test-manifest=../../../../../comm/testing/marionette/unit-tests.ini
-    run-on-projects: built-projects
-
-marionette:
-    description: "Marionette unittest run"
-    treeherder-symbol: Mn
-    max-run-time: 5400
-    e10s: false
-    instance-size: default
-    chunks: 1
-
-marionette-headless:
-    description: "Marionette headless unittest run"
-    treeherder-symbol: MnH
-    max-run-time: 5400
-    e10s: false
-    instance-size: default
-    mozharness:
-        extra-options:
-            - --headless
-

--- a/taskcluster/ci/test/test-sets.yml
+++ b/taskcluster/ci/test/test-sets.yml
@@ -17,13 +17,11 @@
 # Universal tests
 #
 # Tests that run just about everywhere; common-tests is the shared core, with
 # a few add-on test sets that are included or omitted on some platforms.
 
 common-tests:
     - xpcshell
     - mozmill
-    - marionette
-    - marionette-headless
 
 optimized-tests:
     - mochitest-thunderbird

deleted file mode 100644
--- a/testing/marionette/thunderbirdinstance.py
+++ /dev/null
@@ -1,33 +0,0 @@
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at http://mozilla.org/MPL/2.0/
-
-# ALL CHANGES TO THIS FILE MUST HAVE REVIEW FROM A MARIONETTE PEER!
-#
-# The Marionette Python client is used out-of-tree with various builds of
-# Firefox. Removing a preference from this file will cause regressions,
-# so please be careful and get review from a Testing :: Marionette peer
-# before you make any changes to this file.
-
-from __future__ import absolute_import
-
-
-thunderbird_prefs = {
-    # Disable application updates
-    "app.update.disabledForTesting": True,
-
-    # Enable output of dump()
-    "browser.dom.window.dump.enabled": True,
-
-    # Do not show the EULA notification which can interfer with tests
-    "browser.EULA.override": True,
-
-    # Do not start first-run items
-    "mail.provider.suppress_dialog_on_startup": True,
-    "mail.spotlight.firstRunDone": True,
-    "mail.winsearch.firstRunDone": True,
-
-    # Do not open start page
-    "mailnews.start_page.override_url": "about:blank",
-    "mailnews.start_page.url": "about:blank",
-}

deleted file mode 100644
--- a/testing/marionette/unit-tests.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-# mail tests
-[include:../../mail/test/marionette/manifest.ini]