--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -454,33 +454,22 @@ def vc_compiler_path(host):
 
 
 @depends(vc_compiler_path)
 @imports('os')
 def toolchain_search_path(vc_compiler_path):
     if vc_compiler_path:
         result = [os.environ.get('PATH')]
         result.extend(vc_compiler_path)
+        # We're going to alter PATH for good in windows.configure, but we also
+        # need to do it for the valid_compiler() check below.
+        os.environ['PATH'] = os.pathsep.join(result)
         return result
 
 
-# Normally, we'd just have CC, etc. set to absolute paths, but the build system
-# doesn't currently handle properly the case where the paths contain spaces.
-# Additionally, there's the issue described further below in valid_compiler().
-@depends(toolchain_search_path)
-@imports('os')
-def alter_path(toolchain_search_path):
-    if toolchain_search_path:
-        path = os.pathsep.join(toolchain_search_path)
-        os.environ['PATH'] = path
-        return path
-
-set_config('PATH', alter_path)
-
-
 @template
 def default_c_compilers(host_or_target):
     '''Template defining the set of default C compilers for the host and
     target platforms.
     `host_or_target` is either `host` or `target` (the @depends functions
     from init.configure.
     '''
     assert host_or_target in (host, target)

--- a/build/moz.configure/windows.configure
+++ b/build/moz.configure/windows.configure
@@ -114,8 +114,82 @@ def valid_windows_sdk_dir(compiler, wind
 
 add_old_configure_assignment(
     'WINDOWSSDKDIR',
     delayed_getattr(valid_windows_sdk_dir, 'path'))
 add_old_configure_assignment(
     'MOZ_WINSDK_MAXVER',
     depends(valid_windows_sdk_dir)(
         lambda x: '0x%04X0000' % x.version if x else None))
+
+
+option(env='MT', nargs=1, help='Path to the Microsoft Manifest Tool')
+
+@depends_win(valid_windows_sdk_dir)
+@imports(_from='os', _import='environ')
+@imports('platform')
+def sdk_bin_path(valid_windows_sdk_dir):
+    if not valid_windows_sdk_dir:
+        return
+
+    vc_host = {
+        'x86': 'x86',
+        'AMD64': 'x64',
+    }.get(platform.machine())
+
+    result = [
+        environ['PATH'],
+        os.path.join(valid_windows_sdk_dir.path, 'bin', vc_host)
+    ]
+    if vc_host == 'x64':
+        result.append(
+            os.path.join(valid_windows_sdk_dir.path, 'bin', 'x86'))
+    return result
+
+
+# Normally, we'd use `MT` instead of `_MT`, but for now, we want MT to only contain
+# mt.exe.
+mt = check_prog('_MT', depends_win()(lambda: ('mt.exe',)), what='mt',
+                input='MT', paths=sdk_bin_path)
+
+
+# Check that MT is not something unexpected like "magnetic tape manipulation
+# utility".
+@depends_win(mt)
+@checking('whether MT is really Microsoft Manifest Tool', lambda x: bool(x))
+@imports('re')
+@imports('subprocess')
+def valid_mt(path):
+    try:
+        out = subprocess.check_output([path]).splitlines()
+        out = '\n'.join(l for l in out
+                        if 'Microsoft (R) Manifest Tool' in l)
+        if out:
+              m = re.search(r'(?<=[^!-~])[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+',
+                            out)
+              if not m:
+                  raise FatalCheckError(
+                      'Unknown version of the Microsoft Manifest Tool')
+              return namespace(
+                  path=path,
+                  version=Version(m.group(0)),
+              )
+    except subprocess.CalledProcessError:
+        pass
+    raise FatalCheckError('%s is not Microsoft Manifest Tool')
+
+
+set_config('MT', depends_if(valid_mt)(lambda x: os.path.basename(x.path)))
+set_config('MSMANIFEST_TOOL', depends(valid_mt)(lambda x: bool(x)))
+
+
+# Normally, we'd just have CC, etc. set to absolute paths, but the build system
+# doesn't currently handle properly the case where the paths contain spaces.
+# Additionally, there's the issue described in toolchain.configure, in
+# valid_compiler().
+@depends_win(sdk_bin_path)
+@imports('os')
+def alter_path(sdk_bin_path):
+    path = os.pathsep.join(sdk_bin_path)
+    os.environ['PATH'] = path
+    return path
+
+set_config('PATH', alter_path)

--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -48,18 +48,16 @@ dnl ====================================
 NSPR_VERSION=4
 NSPR_MINVER=4.9.2
 
 dnl Set the minimum version of toolkit libs used by mozilla
 dnl ========================================================
 WINDRES_VERSION=2.14.90
 W32API_VERSION=3.14
 
-MSMANIFEST_TOOL=
-
 dnl Set various checks
 dnl ========================================================
 MISSING_X=
 
 dnl Initialize the Pthread test variables early so they can be
 dnl  overridden by each platform.
 dnl ========================================================
 USE_PTHREADS=
@@ -216,36 +214,16 @@ case "$target" in
             # See https://connect.microsoft.com/VisualStudio/feedback/details/1789709/visual-c-2015-runtime-broken-on-windows-server-2003-c-11-magic-statics
             CXXFLAGS="$CXXFLAGS -Zc:threadSafeInit-"
             ;;
         esac
         AC_SUBST(MSVS_VERSION)
         AC_SUBST(MSVC_C_RUNTIME_DLL)
         AC_SUBST(MSVC_CXX_RUNTIME_DLL)
 
-        dnl Ensure that mt.exe is 'Microsoft (R) Manifest Tool',
-        dnl not something else like "magnetic tape manipulation utility".
-        MT=${MT-mt.exe}
-        MSMT_TOOL=`${MT} 2>&1|grep 'Microsoft (R) Manifest Tool'`
-        if test -z "$MSMT_TOOL"; then
-          AC_MSG_ERROR([Microsoft (R) Manifest Tool must be in your \$PATH.])
-        fi
-
-        changequote(,)
-        _MSMT_VER_FILTER='s|.*[^!-~]\([0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*\).*|\1|p'
-        changequote([,])
-        MSMANIFEST_TOOL_VERSION=`echo ${MSMT_TOOL}|sed -ne "$_MSMT_VER_FILTER"`
-        if test -z "$MSMANIFEST_TOOL_VERSION"; then
-          AC_MSG_WARN([Unknown version of the Microsoft (R) Manifest Tool.])
-        fi
-
-        MSMANIFEST_TOOL=1
-        unset MSMT_TOOL
-        AC_SUBST(MT)
-
         # Check linker version
         _LD_FULL_VERSION=`"${LD}" -v 2>&1 | sed -nre "$_MSVC_VER_FILTER"`
         _LD_MAJOR_VERSION=`echo ${_LD_FULL_VERSION} | $AWK -F\. '{ print $1 }'`
         if test "$_LD_MAJOR_VERSION" != "$_CC_SUITE"; then
             AC_MSG_ERROR([The linker major version, $_LD_FULL_VERSION,  does not match the compiler suite version, $_CC_SUITE.])
         fi
 
         INCREMENTAL_LINKER=1
@@ -2433,17 +2411,16 @@ AC_SUBST(DLL_PREFIX)
 AC_SUBST(DLL_SUFFIX)
 AC_DEFINE_UNQUOTED(MOZ_DLL_SUFFIX, "$DLL_SUFFIX")
 AC_SUBST(LIB_SUFFIX)
 AC_SUBST(OBJ_SUFFIX)
 AC_SUBST(BIN_SUFFIX)
 AC_SUBST(IMPORT_LIB_SUFFIX)
 AC_SUBST(USE_N32)
 AC_SUBST(CC_VERSION)
-AC_SUBST(MSMANIFEST_TOOL)
 AC_SUBST(MOZ_LINKER)
 AC_SUBST(WIN32_CONSOLE_EXE_LDFLAGS)
 AC_SUBST(WIN32_GUI_EXE_LDFLAGS)
 
 AC_CHECK_FUNCS(posix_fadvise posix_fallocate)
 
 dnl Set various defines and substitutions
 dnl ========================================================

--- a/old-configure.in
+++ b/old-configure.in
@@ -68,18 +68,16 @@ WINDRES_VERSION=2.14.90
 W32API_VERSION=3.14
 GNOMEUI_VERSION=2.2.0
 GCONF_VERSION=1.2.1
 STARTUP_NOTIFICATION_VERSION=0.8
 DBUS_VERSION=0.60
 SQLITE_VERSION=3.13.0
 FONTCONFIG_VERSION=2.7.0
 
-MSMANIFEST_TOOL=
-
 dnl Set various checks
 dnl ========================================================
 MISSING_X=
 
 dnl Initialize the Pthread test variables early so they can be
 dnl  overridden by each platform.
 dnl ========================================================
 MOZ_USE_PTHREADS=
@@ -342,36 +340,16 @@ case "$target" in
 
         if test -n "$WIN32_REDIST_DIR"; then
           if test ! -d "$WIN32_REDIST_DIR"; then
             AC_MSG_ERROR([Invalid Win32 Redist directory: ${WIN32_REDIST_DIR}])
           fi
           WIN32_REDIST_DIR=`cd "$WIN32_REDIST_DIR" && pwd -W`
         fi
 
-        dnl Ensure that mt.exe is 'Microsoft (R) Manifest Tool',
-        dnl not something else like "magnetic tape manipulation utility".
-        MT=${MT-mt.exe}
-        MSMT_TOOL=`${MT} 2>&1|grep 'Microsoft (R) Manifest Tool'`
-        if test -z "$MSMT_TOOL"; then
-          AC_MSG_ERROR([Microsoft (R) Manifest Tool must be in your \$PATH.])
-        fi
-
-        changequote(,)
-        _MSMT_VER_FILTER='s|.*[^!-~]\([0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*\.[0-9][0-9]*\).*|\1|p'
-        changequote([,])
-        MSMANIFEST_TOOL_VERSION=`echo ${MSMT_TOOL}|sed -ne "$_MSMT_VER_FILTER"`
-        if test -z "$MSMANIFEST_TOOL_VERSION"; then
-          AC_MSG_WARN([Unknown version of the Microsoft (R) Manifest Tool.])
-        fi
-
-        MSMANIFEST_TOOL=1
-        unset MSMT_TOOL
-        AC_SUBST(MT)
-
         # Check linker version
         _LD_FULL_VERSION=`"${LD}" -v 2>&1 | sed -nre "$_MSVC_VER_FILTER"`
         _LD_MAJOR_VERSION=`echo ${_LD_FULL_VERSION} | $AWK -F\. '{ print $1 }'`
         if test "$_LD_MAJOR_VERSION" != "$_CC_SUITE"; then
             AC_MSG_ERROR([The linker major version, $_LD_FULL_VERSION,  does not match the compiler suite version, $_CC_SUITE.])
         fi
 
         INCREMENTAL_LINKER=1
@@ -6501,17 +6479,16 @@ AC_SUBST(DLL_PREFIX)
 AC_SUBST(DLL_SUFFIX)
 AC_DEFINE_UNQUOTED(MOZ_DLL_SUFFIX, "$DLL_SUFFIX")
 AC_SUBST(LIB_SUFFIX)
 AC_SUBST(OBJ_SUFFIX)
 AC_SUBST(BIN_SUFFIX)
 AC_SUBST(IMPORT_LIB_SUFFIX)
 AC_SUBST(USE_N32)
 AC_SUBST(CC_VERSION)
-AC_SUBST(MSMANIFEST_TOOL)
 AC_SUBST(NS_ENABLE_TSF)
 AC_SUBST(WIN32_CONSOLE_EXE_LDFLAGS)
 AC_SUBST(WIN32_GUI_EXE_LDFLAGS)
 
 AC_SUBST(MOZ_VORBIS)
 AC_SUBST(MOZ_TREMOR)
 AC_SUBST(MOZ_FFVPX)
 AC_SUBST_LIST(FFVPX_ASFLAGS)