--- a/build/buildconfig.py
+++ b/build/buildconfig.py
@@ -1,20 +1,19 @@
 # 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/.
 
 import os
 import sys
 from mozbuild.base import MozbuildObject
+from mozbuild.backend.configenvironment import PartialConfigEnvironment
 
 config = MozbuildObject.from_environment()
+partial_config = PartialConfigEnvironment(config.topobjdir)
 
-for var in ('topsrcdir', 'topobjdir', 'defines', 'non_global_defines',
-            'substs'):
+for var in ('topsrcdir', 'topobjdir'):
     value = getattr(config, var)
     setattr(sys.modules[__name__], var, value)
 
-substs = dict(substs)
-
-for var in os.environ:
-    if var not in ('CPP', 'CXXCPP', 'SHELL') and var in substs:
-        substs[var] = os.environ[var]
+for var in ('defines', 'substs', 'get_dependencies'):
+    value = getattr(partial_config, var)
+    setattr(sys.modules[__name__], var, value)

--- a/js/src/builtin/embedjs.py
+++ b/js/src/builtin/embedjs.py
@@ -127,18 +127,17 @@ def messages(jsmsg):
       defines.append("#define %s %i" % (match.group(1), len(defines)))
     else:
       # Make sure that MSG_DEF isn't preceded by whitespace
       assert not line.strip().startswith("MSG_DEF")
   return '\n'.join(defines)
 
 def get_config_defines(buildconfig):
   # Collect defines equivalent to ACDEFINES and add MOZ_DEBUG_DEFINES.
-  env = {key: value for key, value in buildconfig.defines.iteritems()
-         if key not in buildconfig.non_global_defines}
+  env = buildconfig.defines['ALLDEFINES']
   for define in buildconfig.substs['MOZ_DEBUG_DEFINES']:
     env[define] = 1
   return env
 
 def process_inputs(namespace, c_out, msg_file, inputs):
   deps = [path for path in inputs if path.endswith(".h") or path.endswith(".h.js")]
   sources = [path for path in inputs if path.endswith(".js") and not path.endswith(".h.js")]
   assert len(deps) + len(sources) == len(inputs)

--- a/mobile/android/base/generate_build_config.py
+++ b/mobile/android/base/generate_build_config.py
@@ -28,18 +28,18 @@ import sys
 import buildconfig
 
 from mozbuild import preprocessor
 from mozbuild.android_version_code import android_version_code
 
 
 def _defines():
     CONFIG = defaultdict(lambda: None)
-    CONFIG.update(buildconfig.substs)
-    DEFINES = dict(buildconfig.defines)
+    CONFIG.update(buildconfig.substs.iteritems())
+    DEFINES = dict(buildconfig.defines.iteritems())
 
     for var in ('MOZ_ANDROID_ACTIVITY_STREAM'
                 'MOZ_ANDROID_ANR_REPORTER',
                 'MOZ_ANDROID_BEAM',
                 'MOZ_ANDROID_DOWNLOADS_INTEGRATION',
                 'MOZ_ANDROID_DOWNLOAD_CONTENT_SERVICE',
                 'MOZ_ANDROID_EXCLUDE_FONTS',
                 'MOZ_ANDROID_GCM',

--- a/python/mozbuild/mozbuild/action/file_generate.py
+++ b/python/mozbuild/mozbuild/action/file_generate.py
@@ -80,16 +80,20 @@ def main(argv):
                 deps = set()
 
             # Only write out the dependencies if the script was successful
             if not ret:
                 # Add dependencies on any python modules that were imported by
                 # the script.
                 deps |= set(iter_modules_in_path(buildconfig.topsrcdir,
                                                  buildconfig.topobjdir))
+                # Add dependencies on any buildconfig items that were accessed
+                # by the script.
+                deps |= set(buildconfig.get_dependencies())
+
                 mk = Makefile()
                 mk.create_rule([args.output_file]).add_dependencies(deps)
                 with FileAvoidWrite(args.dep_file) as dep_file:
                     mk.dump(dep_file)
         # Even when our file's contents haven't changed, we want to update
         # the file's mtime so make knows this target isn't still older than
         # whatever prerequisite caused it to be built this time around.
         try:

--- a/python/mozbuild/mozbuild/action/generate_symbols_file.py
+++ b/python/mozbuild/mozbuild/action/generate_symbols_file.py
@@ -17,17 +17,17 @@ def generate_symbols_file(output, *args)
     parser = argparse.ArgumentParser()
     parser.add_argument('input')
     parser.add_argument('-D', action=DefinesAction)
     parser.add_argument('-U', action='append', default=[])
     args = parser.parse_args(args)
     input = os.path.abspath(args.input)
 
     pp = Preprocessor()
-    pp.context.update(buildconfig.defines)
+    pp.context.update(buildconfig.defines['ALLDEFINES'])
     if args.D:
         pp.context.update(args.D)
     for undefine in args.U:
         if undefine in pp.context:
             del pp.context[undefine]
     # Hack until MOZ_DEBUG_FLAGS are simply part of buildconfig.defines
     if buildconfig.substs['MOZ_DEBUG']:
         pp.context['DEBUG'] = '1'

--- a/security/generate_certdata.py
+++ b/security/generate_certdata.py
@@ -4,12 +4,12 @@
 # and moz.build `GENERATED_FILES` semantics.
 
 import buildconfig
 import os
 import subprocess
 
 def main(output, *inputs):
     env=dict(os.environ)
-    env['PERL'] = buildconfig.substs['PERL']
+    env['PERL'] = str(buildconfig.substs['PERL'])
     output.write(subprocess.check_output([buildconfig.substs['PYTHON'],
                  inputs[0], inputs[2]], env=env))
     return None

--- a/toolkit/crashreporter/tools/unit-symbolstore.py
+++ b/toolkit/crashreporter/tools/unit-symbolstore.py
@@ -145,17 +145,17 @@ class TestCopyDebug(HelperMixin, unittes
         d = symbolstore.GetPlatformSpecificDumper(dump_syms="dump_syms",
                                                   symbol_path=self.symbol_dir,
                                                   copy_debug=True,
                                                   archs="abc xyz")
         d.CopyDebug = mock_copy_debug
         d.Process(os.path.join(self.test_dir, add_extension(["foo"])[0]))
         self.assertEqual(1, len(copied))
 
-    @patch.dict('buildconfig.substs', {'MAKECAB': 'makecab'})
+    @patch.dict('buildconfig.substs._dict', {'MAKECAB': 'makecab'})
     def test_copy_debug_copies_binaries(self):
         """
         Test that CopyDebug copies binaries as well on Windows.
         """
         test_file = os.path.join(self.test_dir, 'foo.dll')
         write_dll(test_file)
         code_file = 'foo.dll'
         code_id = 'abc123'

--- a/toolkit/mozapps/installer/find-dupes.py
+++ b/toolkit/mozapps/installer/find-dupes.py
@@ -97,17 +97,17 @@ def main():
     parser.add_argument('directory',
                         help='The directory to check for duplicates in')
 
     args = parser.parse_args()
 
     allowed_dupes = []
     for filename in args.dupes_files:
         pp = Preprocessor()
-        pp.context.update(buildconfig.defines)
+        pp.context.update(buildconfig.defines['ALLDEFINES'])
         if args.D:
             pp.context.update(args.D)
         for undefine in args.U:
             if undefine in pp.context:
                 del pp.context[undefine]
         pp.out = StringIO()
         pp.do_filter('substitution')
         pp.do_include(filename)

--- a/toolkit/mozapps/installer/packager.py
+++ b/toolkit/mozapps/installer/packager.py
@@ -221,17 +221,17 @@ def main():
                         help='Manifest file name')
     parser.add_argument('source', help='Source directory')
     parser.add_argument('destination', help='Destination directory')
     parser.add_argument('--non-resource', nargs='+', metavar='PATTERN',
                         default=[],
                         help='Extra files not to be considered as resources')
     args = parser.parse_args()
 
-    defines = dict(buildconfig.defines)
+    defines = dict(buildconfig.defines['ALLDEFINES'])
     if args.ignore_errors:
         errors.ignore_errors()
 
     if args.defines:
         for name, value in [split_define(d) for d in args.defines]:
             defines[name] = value
 
     compress = {