--- a/testing/mozharness/configs/builds/taskcluster_firefox_win32_clang.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win32_clang.py
@@ -24,21 +24,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_win32_clang_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win32_clang_debug.py
@@ -24,21 +24,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_win32_qr_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win32_qr_debug.py
@@ -25,21 +25,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_win32_qr_opt.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win32_qr_opt.py
@@ -25,21 +25,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_win64_asan_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win64_asan_debug.py
@@ -24,21 +24,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_win64_asan_opt.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win64_asan_opt.py
@@ -24,21 +24,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_win64_clang.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win64_clang.py
@@ -24,21 +24,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_win64_clang_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win64_clang_debug.py
@@ -24,21 +24,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_win64_qr_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win64_qr_debug.py
@@ -20,21 +20,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_win64_qr_opt.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_win64_qr_opt.py
@@ -20,21 +20,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_addondevel.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_addondevel.py
@@ -25,21 +25,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': False,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_debug.py
@@ -25,21 +25,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_opt.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_windows_32_opt.py
@@ -25,21 +25,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_addondevel.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_addondevel.py
@@ -26,21 +26,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': False,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_debug.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_debug.py
@@ -25,21 +25,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_opt.py
+++ b/testing/mozharness/configs/builds/taskcluster_firefox_windows_64_opt.py
@@ -25,21 +25,16 @@ config = {
     'exes': {
         'python2.7': sys.executable,
         'virtualenv': [
             sys.executable,
             os.path.join(
                 os.getcwd(), 'build', 'src', 'python', 'virtualenv', 'virtualenv.py'
             )
         ],
-        'mach-build': [
-            os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
-            os.path.join(os.getcwd(), 'build', 'src', 'mach'),
-            '--log-no-times', 'build', '-v'
-        ],
     },
     'app_ini_path': '%(obj_dir)s/dist/bin/application.ini',
     # decides whether we want to use moz_sign_cmd in env
     'enable_signing': True,
     'enable_ccache': False,
     'vcs_share_base': os.path.join('y:', os.sep, 'hg-shared'),
     'objdir': 'obj-firefox',
     'tooltool_script': [

--- a/testing/mozharness/mozharness/mozilla/building/buildbase.py
+++ b/testing/mozharness/mozharness/mozilla/building/buildbase.py
@@ -1633,22 +1633,26 @@ or run without that action (ie: --no-{ac
         dirs = self.query_abs_dirs()
         buildprops = os.path.join(dirs['base_work_dir'], 'buildprops.json')
         # not finding buildprops is not an error outside of buildbot
         if os.path.exists(buildprops):
             self.copyfile(
                 buildprops,
                 os.path.join(dirs['abs_work_dir'], 'buildprops.json'))
 
-        # use mh config override for mach build wrapper, if it exists
-        python = self.query_exe('python2.7')
-        default_mach_build = [python, 'mach', '--log-no-times', 'build', '-v']
-        mach_build = self.query_exe('mach-build', default=default_mach_build)
+        if 'MOZILLABUILD' in os.environ:
+            mach = [
+                os.path.join(os.environ['MOZILLABUILD'], 'msys', 'bin', 'bash.exe'),
+                os.path.join(dirs['abs_src_dir'], 'mach')
+            ]
+        else:
+            mach = [self.query_exe('python2.7'), 'mach']
+
         return_code = self.run_command_m(
-            command=mach_build,
+            command=mach + ['--log-no-times', 'build', '-v'],
             cwd=dirs['abs_src_dir'],
             env=env,
             output_timeout=self.config.get('max_build_output_timeout', 60 * 40)
         )
         if return_code:
             self.return_code = self.worst_level(
                 EXIT_STATUS_DICT[TBPL_FAILURE],  self.return_code,
                 AUTOMATION_EXIT_CODES[::-1]