--- a/testing/mozharness/configs/awsy/taskcluster_windows_config.py
+++ b/testing/mozharness/configs/awsy/taskcluster_windows_config.py
@@ -6,17 +6,16 @@ external_tools_path = os.path.join(
     os.path.abspath(os.path.dirname(os.path.dirname(mozharness.__file__))),
     'external_tools',
 )
 
 config = {
     "virtualenv_path": 'venv',
     "exes": {
         'python': sys.executable,
-        'mozinstall': ['build/venv/scripts/python', 'build/venv/scripts/mozinstall-script.py'],
         'hg': os.path.join(os.environ['PROGRAMFILES'], 'Mercurial', 'hg')
     },
     "find_links": [
         "http://pypi.pub.build.mozilla.org/pub",
     ],
     "pip_index": False,
 
     "download_minidump_stackwalk": True,

--- a/testing/mozharness/configs/firefox_ui_tests/taskcluster_windows.py
+++ b/testing/mozharness/configs/firefox_ui_tests/taskcluster_windows.py
@@ -3,17 +3,16 @@
 import os
 import sys
 
 
 config = {
     "virtualenv_path": 'venv',
     "exes": {
         'python': sys.executable,
-        'mozinstall': ['build/venv/scripts/python', 'build/venv/scripts/mozinstall-script.py'],
         'hg': os.path.join(os.environ['PROGRAMFILES'], 'Mercurial', 'hg')
     },
 
     "find_links": [
         "http://pypi.pub.build.mozilla.org/pub",
     ],
     "pip_index": False,
 

--- a/testing/mozharness/configs/marionette/windows_config.py
+++ b/testing/mozharness/configs/marionette/windows_config.py
@@ -5,18 +5,16 @@ config = {
     # marionette options
     "marionette_address": "localhost:2828",
     "test_manifest": "unit-tests.ini",
 
     "virtualenv_path": 'venv',
     "exes": {
         'python': 'c:/mozilla-build/python27/python',
         'hg': 'c:/mozilla-build/hg/hg',
-        'mozinstall': ['%s/build/venv/scripts/python' % os.getcwd(),
-                       '%s/build/venv/scripts/mozinstall-script.py' % os.getcwd()],
     },
 
     "find_links": [
         "http://pypi.pvt.build.mozilla.org/pub",
         "http://pypi.pub.build.mozilla.org/pub",
     ],
     "pip_index": False,
 

--- a/testing/mozharness/configs/marionette/windows_taskcluster_config.py
+++ b/testing/mozharness/configs/marionette/windows_taskcluster_config.py
@@ -5,17 +5,16 @@ import sys
 config = {
     # marionette options
     "marionette_address": "localhost:2828",
     "test_manifest": "unit-tests.ini",
 
     "virtualenv_path": 'venv',
     "exes": {
         'python': sys.executable,
-        'mozinstall': ['build/venv/scripts/python', 'build/venv/scripts/mozinstall-script.py'],
         'hg': os.path.join(os.environ['PROGRAMFILES'], 'Mercurial', 'hg')
     },
 
     "find_links": [
         "http://pypi.pub.build.mozilla.org/pub",
     ],
     "pip_index": False,
 

--- a/testing/mozharness/configs/talos/windows_config.py
+++ b/testing/mozharness/configs/talos/windows_config.py
@@ -14,18 +14,16 @@ config = {
     "pip_index": False,
     "find_links": [
         "http://pypi.pvt.build.mozilla.org/pub",
         "http://pypi.pub.build.mozilla.org/pub",
     ],
     "virtualenv_modules": ['pywin32', 'talos', 'mozinstall'],
     "exes": {
         'python': PYTHON,
-        'mozinstall': ['%s/scripts/python' % VENV_PATH,
-                       '%s/scripts/mozinstall-script.py' % VENV_PATH],
         'hg': os.path.join(os.environ['PROGRAMFILES'], 'Mercurial', 'hg'),
         'tooltool.py': [PYTHON, os.path.join(os.environ['MOZILLABUILD'], 'tooltool.py')],
     },
     "title": socket.gethostname().split('.')[0],
     "default_actions": [
         "clobber",
         "read-buildbot-config",
         "download-and-extract",

--- a/testing/mozharness/configs/talos/windows_taskcluster_config.py
+++ b/testing/mozharness/configs/talos/windows_taskcluster_config.py
@@ -13,18 +13,16 @@ config = {
     "virtualenv_path": VENV_PATH,
     "pip_index": False,
     "find_links": [
         "http://pypi.pub.build.mozilla.org/pub",
     ],
     "virtualenv_modules": ['pypiwin32', 'talos', 'mozinstall'],
     "exes": {
         'python': PYTHON,
-        'mozinstall': ['%s/scripts/python' % VENV_PATH,
-                       '%s/scripts/mozinstall-script.py' % VENV_PATH],
         'hg': os.path.join(os.environ['PROGRAMFILES'], 'Mercurial', 'hg'),
     },
     "title": socket.gethostname().split('.')[0],
     "default_actions": [
         "populate-webroot",
         "create-virtualenv",
         "install",
         "setup-mitmproxy",

--- a/testing/mozharness/configs/talos/windows_vm_config.py
+++ b/testing/mozharness/configs/talos/windows_vm_config.py
@@ -14,18 +14,16 @@ config = {
     "pip_index": False,
     "find_links": [
         "http://pypi.pvt.build.mozilla.org/pub",
         "http://pypi.pub.build.mozilla.org/pub",
     ],
     "virtualenv_modules": ['pywin32', 'talos', 'mozinstall'],
     "exes": {
         'python': PYTHON,
-        'mozinstall': ['%s/scripts/python' % VENV_PATH,
-                       '%s/scripts/mozinstall-script.py' % VENV_PATH],
         'hg': os.path.join(os.environ['PROGRAMFILES'], 'Mercurial', 'hg'),
     },
     "title": socket.gethostname().split('.')[0],
     "default_actions": [
         "clobber",
         "read-buildbot-config",
         "download-and-extract",
         "populate-webroot",

--- a/testing/mozharness/configs/unittests/win_taskcluster_unittest.py
+++ b/testing/mozharness/configs/unittests/win_taskcluster_unittest.py
@@ -19,17 +19,16 @@ DESKTOP_VISUALFX_THEME = {
 TASKBAR_AUTOHIDE_REG_PATH = {
     'Windows 7': 'HKCU:SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\StuckRects2',
     'Windows 10': 'HKCU:SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\StuckRects3'
 }.get('{} {}'.format(platform.system(), platform.release()))
 #####
 config = {
     "exes": {
         'python': sys.executable,
-        'mozinstall': ['build/venv/scripts/python', 'build/venv/scripts/mozinstall-script.py'],
         'hg': os.path.join(os.environ['PROGRAMFILES'], 'Mercurial', 'hg')
     },
     ###
     "installer_path": INSTALLER_PATH,
     "binary_path": BINARY_PATH,
     "xpcshell_name": XPCSHELL_NAME,
     "virtualenv_modules": ['pypiwin32'],
     "virtualenv_path": 'venv',

--- a/testing/mozharness/configs/unittests/win_unittest.py
+++ b/testing/mozharness/configs/unittests/win_unittest.py
@@ -10,18 +10,16 @@ EXE_SUFFIX = '.exe'
 DISABLE_SCREEN_SAVER = False
 ADJUST_MOUSE_AND_SCREEN = True
 #####
 config = {
     "buildbot_json_path": "buildprops.json",
     "exes": {
         'python': sys.executable,
         'hg': 'c:/mozilla-build/hg/hg',
-        'mozinstall': ['%s/build/venv/scripts/python' % os.getcwd(),
-                       '%s/build/venv/scripts/mozinstall-script.py' % os.getcwd()],
     },
     ###
     "installer_path": INSTALLER_PATH,
     "binary_path": BINARY_PATH,
     "xpcshell_name": XPCSHELL_NAME,
     "virtualenv_path": 'venv',
     "virtualenv_modules": ['pywin32'],
 

--- a/testing/mozharness/configs/web_platform_tests/prod_config_windows.py
+++ b/testing/mozharness/configs/web_platform_tests/prod_config_windows.py
@@ -18,18 +18,16 @@ config = {
         "--host-key-path=%(test_path)s/certs/web-platform.test.key",
         "--host-cert-path=%(test_path)s/certs/web-platform.test.pem",
         "--certutil-binary=%(test_install_path)s/bin/certutil",
     ],
 
     "exes": {
         'python': sys.executable,
         'hg': 'c:/mozilla-build/hg/hg',
-        'mozinstall': ['%s/build/venv/scripts/python' % os.getcwd(),
-                       '%s/build/venv/scripts/mozinstall-script.py' % os.getcwd()],
     },
 
     "find_links": [
         "http://pypi.pvt.build.mozilla.org/pub",
         "http://pypi.pub.build.mozilla.org/pub",
     ],
 
     "pip_index": False,

--- a/testing/mozharness/configs/web_platform_tests/prod_config_windows_taskcluster.py
+++ b/testing/mozharness/configs/web_platform_tests/prod_config_windows_taskcluster.py
@@ -17,17 +17,16 @@ config = {
         "--ca-cert-path=%(test_path)s/certs/cacert.pem",
         "--host-key-path=%(test_path)s/certs/web-platform.test.key",
         "--host-cert-path=%(test_path)s/certs/web-platform.test.pem",
         "--certutil-binary=%(test_install_path)s/bin/certutil",
     ],
 
     "exes": {
         'python': sys.executable,
-        'mozinstall': ['build/venv/scripts/python', 'build/venv/scripts/mozinstall-script.py'],
         'hg': os.path.join(os.environ['PROGRAMFILES'], 'Mercurial', 'hg')
     },
 
     "find_links": [
         "http://pypi.pub.build.mozilla.org/pub",
     ],
 
     "pip_index": False,

--- a/testing/mozharness/configs/web_platform_tests/test_config_windows.py
+++ b/testing/mozharness/configs/web_platform_tests/test_config_windows.py
@@ -1,33 +1,30 @@
 # ***** BEGIN LICENSE BLOCK *****
 # 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/.
 # ***** END LICENSE BLOCK *****
 
-import os
 import sys
 
 config = {
     "options": [
         "--prefs-root=%(test_path)s/prefs",
         "--processes=1",
         "--config=%(test_path)s/wptrunner.ini",
         "--ca-cert-path=%(test_path)s/certs/cacert.pem",
         "--host-key-path=%(test_path)s/certs/web-platform.test.key",
         "--host-cert-path=%(test_path)s/certs/web-platform.test.pem",
         "--certutil-binary=%(test_install_path)s/bin/certutil",
     ],
 
     "exes": {
         'python': sys.executable,
         'hg': 'c:/mozilla-build/hg/hg',
-        'mozinstall': ['%s/build/venv/scripts/python' % os.getcwd(),
-                       '%s/build/venv/scripts/mozinstall-script.py' % os.getcwd()],
     },
 
     "default_actions": [
         'clobber',
         'download-and-extract',
         'create-virtualenv',
         'pull',
         'install',

--- a/testing/mozharness/mozharness/mozilla/testing/testbase.py
+++ b/testing/mozharness/mozharness/mozilla/testing/testbase.py
@@ -585,17 +585,17 @@ 2. running the download-and-extract acti
 """)
         if not self.is_python_package_installed("mozInstall"):
             self.fatal("""Can't call install() without mozinstall!
 Did you run with --create-virtualenv? Is mozinstall in virtualenv_modules?""")
 
     def install_app(self, app=None, target_dir=None, installer_path=None):
         """ Dependent on mozinstall """
         # install the application
-        cmd = self.query_exe("mozinstall", default=self.query_python_path("mozinstall"), return_type="list")
+        cmd = [self.query_python_path("mozinstall")]
         if app:
             cmd.extend(['--app', app])
         # Remove the below when we no longer need to support mozinstall 0.3
         self.info("Detecting whether we're running mozinstall >=1.0...")
         output = self.get_output_from_command(cmd + ['-h'])
         if '--source' in output:
             cmd.append('--source')
         # End remove