--- a/build/autoconf/python-virtualenv.m4
+++ b/build/autoconf/python-virtualenv.m4
@@ -19,17 +19,17 @@ fi
 
 _virtualenv_topsrcdir=
 _virtualenv_populate_path=
 
 dnl If this is a mozilla-central, we'll find the virtualenv in the top
 dnl source directory. If this is a SpiderMonkey build, we assume we're at
 dnl js/src and try to find the virtualenv from the mozilla-central root.
 for base in $MOZILLA_CENTRAL_PATH $_topsrcdir $_topsrcdir/../..; do
-  possible=$base/build/virtualenv/populate_virtualenv.py
+  possible=$base/python/mozbuild/mozbuild/virtualenv.py
 
   if test -e $possible; then
     _virtualenv_topsrcdir=$base
     _virtualenv_populate_path=$possible
     break
   fi
 done
 
@@ -48,17 +48,18 @@ mozilla-central and relaunch configure.]
 fi
 
 if test -z $DONT_POPULATE_VIRTUALENV; then
   AC_MSG_RESULT([Creating Python environment])
   dnl This verifies our Python version is sane and ensures the Python
   dnl virtualenv is present and up to date. It sanitizes the environment
   dnl for us, so we don't need to clean anything out.
   $PYTHON $_virtualenv_populate_path \
-    $_virtualenv_topsrcdir $MOZ_BUILD_ROOT $MOZ_BUILD_ROOT/_virtualenv || exit 1
+    $_virtualenv_topsrcdir $MOZ_BUILD_ROOT $MOZ_BUILD_ROOT/_virtualenv \
+    $_virtualenv_topsrcdir/build/virtualenv_packages.txt || exit 1
 
   case "$host_os" in
   mingw*)
     PYTHON=`cd $MOZ_BUILD_ROOT && pwd -W`/_virtualenv/Scripts/python.exe
     ;;
   *)
     PYTHON=$MOZ_BUILD_ROOT/_virtualenv/bin/python
     ;;

rename from build/virtualenv/packages.txt
rename to build/virtualenv_packages.txt

--- a/client.mk
+++ b/client.mk
@@ -320,18 +320,18 @@ EXTRA_CONFIG_DEPS := \
 CONFIG_STATUS_DEPS := \
   $(wildcard $(TOPSRCDIR)/*/confvars.sh) \
   $(CONFIGURES) \
   $(TOPSRCDIR)/CLOBBER \
   $(TOPSRCDIR)/nsprpub/configure \
   $(TOPSRCDIR)/config/milestone.txt \
   $(TOPSRCDIR)/js/src/config/milestone.txt \
   $(TOPSRCDIR)/browser/config/version.txt \
-  $(TOPSRCDIR)/build/virtualenv/packages.txt \
-  $(TOPSRCDIR)/build/virtualenv/populate_virtualenv.py \
+  $(TOPSRCDIR)/build/virtualenv_packages.txt \
+  $(TOPSRCDIR)/python/mozbuild/mozbuild/virtualenv.py \
   $(TOPSRCDIR)/testing/mozbase/packages.txt \
   $(NULL)
 
 CONFIGURE_ENV_ARGS += \
   MAKE="$(MAKE)" \
   $(NULL)
 
 # configure uses the program name to determine @srcdir@. Calling it without

--- a/js/src/build/autoconf/python-virtualenv.m4
+++ b/js/src/build/autoconf/python-virtualenv.m4
@@ -19,17 +19,17 @@ fi
 
 _virtualenv_topsrcdir=
 _virtualenv_populate_path=
 
 dnl If this is a mozilla-central, we'll find the virtualenv in the top
 dnl source directory. If this is a SpiderMonkey build, we assume we're at
 dnl js/src and try to find the virtualenv from the mozilla-central root.
 for base in $MOZILLA_CENTRAL_PATH $_topsrcdir $_topsrcdir/../..; do
-  possible=$base/build/virtualenv/populate_virtualenv.py
+  possible=$base/python/mozbuild/mozbuild/virtualenv.py
 
   if test -e $possible; then
     _virtualenv_topsrcdir=$base
     _virtualenv_populate_path=$possible
     break
   fi
 done
 
@@ -48,17 +48,18 @@ mozilla-central and relaunch configure.]
 fi
 
 if test -z $DONT_POPULATE_VIRTUALENV; then
   AC_MSG_RESULT([Creating Python environment])
   dnl This verifies our Python version is sane and ensures the Python
   dnl virtualenv is present and up to date. It sanitizes the environment
   dnl for us, so we don't need to clean anything out.
   $PYTHON $_virtualenv_populate_path \
-    $_virtualenv_topsrcdir $MOZ_BUILD_ROOT $MOZ_BUILD_ROOT/_virtualenv || exit 1
+    $_virtualenv_topsrcdir $MOZ_BUILD_ROOT $MOZ_BUILD_ROOT/_virtualenv \
+    $_virtualenv_topsrcdir/build/virtualenv_packages.txt || exit 1
 
   case "$host_os" in
   mingw*)
     PYTHON=`cd $MOZ_BUILD_ROOT && pwd -W`/_virtualenv/Scripts/python.exe
     ;;
   *)
     PYTHON=$MOZ_BUILD_ROOT/_virtualenv/bin/python
     ;;

rename from build/virtualenv/populate_virtualenv.py
rename to python/mozbuild/mozbuild/virtualenv.py
--- a/build/virtualenv/populate_virtualenv.py
+++ b/python/mozbuild/mozbuild/virtualenv.py
@@ -361,17 +361,17 @@ class VirtualenvManager(object):
         """
 
         self.create()
 
         # We need to populate the virtualenv using the Python executable in
         # the virtualenv for paths to be proper.
 
         args = [self.python_path, __file__, 'populate', self.topsrcdir,
-            self.topobjdir, self.virtualenv_root]
+            self.topobjdir, self.virtualenv_root, self.manifest_path]
 
         result = subprocess.call(args, stdout=self.log_handle,
             stderr=subprocess.STDOUT, cwd=self.topsrcdir)
 
         if result != 0:
             raise Exception('Error populating virtualenv.')
 
         os.utime(self.activate_path, None)
@@ -404,36 +404,29 @@ def verify_python_version(log_handle):
             log_handle.write(UPGRADE_WINDOWS)
         else:
             log_handle.write(UPGRADE_OTHER)
 
         sys.exit(1)
 
 
 if __name__ == '__main__':
-    if len(sys.argv) < 4:
-        print('Usage: populate_virtualenv.py /path/to/topsrcdir /path/to/topobjdir /path/to/virtualenv')
+    if len(sys.argv) < 5:
+        print('Usage: populate_virtualenv.py /path/to/topsrcdir /path/to/topobjdir /path/to/virtualenv /path/to/virtualenv_manifest')
         sys.exit(1)
 
     verify_python_version(sys.stdout)
 
-    topsrcdir = sys.argv[1]
-    topobjdir = sys.argv[2]
-    virtualenv_path = sys.argv[3]
+    topsrcdir, topobjdir, virtualenv_path, manifest_path = sys.argv[1:5]
     populate = False
 
     # This should only be called internally.
     if sys.argv[1] == 'populate':
         populate = True
-        topsrcdir = sys.argv[2]
-        topobjdir = sys.argv[3]
-        virtualenv_path = sys.argv[4]
-
-    # path to default packages.txt
-    manifest_path = os.path.join(topsrcdir, 'build', 'virtualenv', 'packages.txt')
+        topsrcdir, topobjdir, virtualenv_path, manifest_path = sys.argv[2:]
 
     manager = VirtualenvManager(topsrcdir, topobjdir, virtualenv_path,
         sys.stdout, manifest_path)
 
     if populate:
         manager.populate()
     else:
         manager.ensure()