--- a/js/src/Makefile.in
+++ b/js/src/Makefile.in
@@ -13,46 +13,18 @@ ifneq ($(make_min_ver),$(firstword $(sor
 endif
 
 DASH_R		= -r
 
 # Define keyword generator before rules.mk, see bug 323979 comment 50
 
 USE_HOST_CXX = 1
 
-# Ensure symbol versions of shared library on Linux do not conflict
-# with those in libxul.
-ifeq (Linux,$(OS_TARGET))
-OS_LDFLAGS += -Wl,-version-script,symverscript
-
-symverscript: symverscript.in
-	$(call py_action,preprocessor, \
-		-DVERSION='$(subst -,_,$(LIBRARY_NAME))' $< -o $@)
-
-EXTRA_DEPS += symverscript
-endif
-
 include $(topsrcdir)/config/rules.mk
 
-# check_vanilla_allocations.py is tailored to Linux, so only run it there.
-# That should be enough to catch any problems.
-check-vanilla-allocations:
-	$(PYTHON) $(topsrcdir)/config/check_vanilla_allocations.py $(REAL_LIBRARY)
-
-# The "aggressive" variant will likely fail on some compiler/platform
-# combinations, but is worth running by hand every once in a while.
-check-vanilla-allocations-aggressive:
-	$(PYTHON) $(topsrcdir)/config/check_vanilla_allocations.py --aggressive $(REAL_LIBRARY)
-
-ifeq ($(OS_ARCH),Linux)
-ifeq (,$(filter -flto,$(CFLAGS) $(CXXFLAGS) $(LDFLAGS)))
-check:: check-vanilla-allocations
-endif
-endif
-
 # Help ensure that the number of OOM errors in SpiderMonkey doesn't increase.
 # If the number of OOM errors changes, update the number below. We intend this
 # number to go down over time, by fixing OOMs.
 check-ooms:
 	$(wildcard $(RUN_TEST_PROGRAM)) $(PYTHON) -u $(topsrcdir)/config/find_OOM_errors.py --regression 125
 
 ifeq ($(MOZ_DEBUG),1)
 #check:: check-ooms
@@ -157,72 +129,18 @@ ifeq ($(TARGET_CPU),sparc)
 ifdef GNU_CC
 CFLAGS   += -mcpu=v9
 CXXFLAGS += -mcpu=v9
 endif # GNU_CC
 
 endif
 endif
 
-SCRIPTS = $(JS_CONFIG_NAME)
-
-$(LIBRARY_NAME).pc: js.pc
-	cp $^ $@
-
-install:: $(LIBRARY_NAME).pc
-	$(SYSINSTALL) $^ $(DESTDIR)$(libdir)/pkgconfig
-
-install:: js-config.h
-	$(SYSINSTALL) $^ $(DESTDIR)$(includedir)
-
-######################################################
-# BEGIN SpiderMonkey header installation
-#
-# Mozilla/Gecko/Firefox mostly doesn't concern itself with defining a sensible
-# install target, because it's shipping primarily packaged builds.  And even if
-# it did, those builds wouldn't really have reason to include header files.  So
-# we have to install public headers ourselves, rather than using something from
-# config/rules.mk or similar.
-#
-# The overall directory structure of the installed headers looks like so:
-#
-#   $(includedir)/
-#      $(LIBRARY_NAME)/
-#        jsapi.h, jspubtd.h, etc. (all of EXPORTS)
-#        js/
-#          js/public/* headers (all are public)
-#        ds/
-#          js/src/ds/* public headers
-#        gc/
-#          js/src/gc/* public headers
-#        mozilla/
-#          mfbt headers
-#
-
 install::
-	$(call py_action,process_install_manifest,--no-remove --no-symlinks $(DESTDIR)$(includedir) $(DEPTH)/_build_manifests/install/dist_include)
-
-#
-# END SpiderMonkey header installation
-#############################################
-
-install:: $(SCRIPTS)
-	$(SYSINSTALL) $^ $(DESTDIR)$(bindir)
-
-install:: $(REAL_LIBRARY) $(SHARED_LIBRARY) $(IMPORT_LIBRARY)
-ifneq (,$(REAL_LIBRARY))
-	$(SYSINSTALL) $(REAL_LIBRARY) $(DESTDIR)$(libdir)
-	mv -f $(DESTDIR)$(libdir)/$(REAL_LIBRARY) $(subst $(STATIC_LIBRARY_NAME),$(LIBRARY_NAME),$(DESTDIR)$(libdir)/$(REAL_LIBRARY))
-endif
-ifneq (,$(SHARED_LIBRARY))
-	$(SYSINSTALL) $(SHARED_LIBRARY) $(DESTDIR)$(libdir)
-endif
-ifneq (,$(IMPORT_LIBRARY))
-	$(SYSINSTALL) $(IMPORT_LIBRARY) $(DESTDIR)$(libdir)
-endif
+	$(MAKE) -C build install
 	$(MAKE) -C shell install
 
 ifdef HAVE_DTRACE
 javascript-trace.h: $(srcdir)/devtools/javascript-trace.d
 	dtrace -x nolibs -h -s $(srcdir)/devtools/javascript-trace.d -o javascript-trace.h.in
 	sed -e 's/if _DTRACE_VERSION/ifdef INCLUDE_MOZILLA_DTRACE/' \
 	    -e '/const/!s/char \*/const char */g' \
 	    javascript-trace.h.in > javascript-trace.h

--- a/js/src/build.rs
+++ b/js/src/build.rs
@@ -31,17 +31,17 @@ fn main() {
         .stdout(Stdio::inherit())
         .stderr(Stdio::inherit());
     println!("Running command: {:?}", cmd);
     let result = cmd
         .status()
         .expect("Should spawn autospider OK");
     assert!(result.success(), "autospider should exit OK");
 
-    println!("cargo:rustc-link-search=native={}/js/src", out_dir);
+    println!("cargo:rustc-link-search=native={}/js/src/build", out_dir);
 
     if target.contains("windows") {
         println!("cargo:rustc-link-lib=winmm");
         if target.contains("gnu") {
             println!("cargo:rustc-link-lib=stdc++");
         }
     } else {
         println!("cargo:rustc-link-lib=stdc++");

new file mode 100644
--- /dev/null
+++ b/js/src/build/Makefile.in
@@ -0,0 +1,92 @@
+# -*- Mode: makefile -*-
+#
+# 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/.
+
+# Ensure symbol versions of shared library on Linux do not conflict
+# with those in libxul.
+ifeq (Linux,$(OS_TARGET))
+OS_LDFLAGS += -Wl,-version-script,symverscript
+
+symverscript: symverscript.in
+	$(call py_action,preprocessor, \
+		-DVERSION='$(subst -,_,$(LIBRARY_NAME))' $< -o $@)
+
+EXTRA_DEPS += symverscript
+endif
+
+include $(topsrcdir)/config/rules.mk
+
+# check_vanilla_allocations.py is tailored to Linux, so only run it there.
+# That should be enough to catch any problems.
+check-vanilla-allocations:
+	$(PYTHON) $(topsrcdir)/config/check_vanilla_allocations.py $(REAL_LIBRARY)
+
+# The "aggressive" variant will likely fail on some compiler/platform
+# combinations, but is worth running by hand every once in a while.
+check-vanilla-allocations-aggressive:
+	$(PYTHON) $(topsrcdir)/config/check_vanilla_allocations.py --aggressive $(REAL_LIBRARY)
+
+ifeq ($(OS_ARCH),Linux)
+ifeq (,$(filter -flto,$(CFLAGS) $(CXXFLAGS) $(LDFLAGS)))
+check:: check-vanilla-allocations
+endif
+endif
+
+SCRIPTS = $(JS_CONFIG_NAME)
+
+$(LIBRARY_NAME).pc: js.pc
+	cp $^ $@
+
+install:: $(LIBRARY_NAME).pc
+	$(SYSINSTALL) $^ $(DESTDIR)$(libdir)/pkgconfig
+
+install:: ../js-config.h
+	$(SYSINSTALL) $^ $(DESTDIR)$(includedir)
+
+######################################################
+# BEGIN SpiderMonkey header installation
+#
+# Mozilla/Gecko/Firefox mostly doesn't concern itself with defining a sensible
+# install target, because it's shipping primarily packaged builds.  And even if
+# it did, those builds wouldn't really have reason to include header files.  So
+# we have to install public headers ourselves, rather than using something from
+# config/rules.mk or similar.
+#
+# The overall directory structure of the installed headers looks like so:
+#
+#   $(includedir)/
+#      $(LIBRARY_NAME)/
+#        jsapi.h, jspubtd.h, etc. (all of EXPORTS)
+#        js/
+#          js/public/* headers (all are public)
+#        ds/
+#          js/src/ds/* public headers
+#        gc/
+#          js/src/gc/* public headers
+#        mozilla/
+#          mfbt headers
+#
+
+install::
+	$(call py_action,process_install_manifest,--no-remove --no-symlinks $(DESTDIR)$(includedir) $(DEPTH)/_build_manifests/install/dist_include)
+
+#
+# END SpiderMonkey header installation
+#############################################
+
+install:: $(SCRIPTS)
+	$(SYSINSTALL) $^ $(DESTDIR)$(bindir)
+
+install:: $(REAL_LIBRARY) $(SHARED_LIBRARY) $(IMPORT_LIBRARY)
+ifneq (,$(REAL_LIBRARY))
+	$(SYSINSTALL) $(REAL_LIBRARY) $(DESTDIR)$(libdir)
+	mv -f $(DESTDIR)$(libdir)/$(REAL_LIBRARY) $(subst $(STATIC_LIBRARY_NAME),$(LIBRARY_NAME),$(DESTDIR)$(libdir)/$(REAL_LIBRARY))
+endif
+ifneq (,$(SHARED_LIBRARY))
+	$(SYSINSTALL) $(SHARED_LIBRARY) $(DESTDIR)$(libdir)
+endif
+ifneq (,$(IMPORT_LIBRARY))
+	$(SYSINSTALL) $(IMPORT_LIBRARY) $(DESTDIR)$(libdir)
+endif

rename from js/src/js-config.in
rename to js/src/build/js-config.in

rename from js/src/js.pc.in
rename to js/src/build/js.pc.in

new file mode 100644
--- /dev/null
+++ b/js/src/build/moz.build
@@ -0,0 +1,77 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+CONFIGURE_SUBST_FILES += [
+    'js-config',
+    'js.pc',
+]
+
+if not CONFIG['JS_STANDALONE']:
+    LIBRARY_DEFINES['MOZ_HAS_MOZGLUE'] = True
+
+# JavaScript must be built shared, even for static builds, as it is used by
+# other modules which are always built shared. Failure to do so results in
+# the js code getting copied into xpinstall and jsd as well as mozilla-bin,
+# and then the static data cells used for locking no longer work.
+#
+# In fact, we now build both a static and a shared library, as the
+# JS shell would like to link to the static library.
+
+if CONFIG['JS_SHARED_LIBRARY']:
+    GeckoSharedLibrary('js', linkage=None)
+    SHARED_LIBRARY_NAME = CONFIG['JS_LIBRARY_NAME']
+else:
+    Library('js')
+
+FORCE_STATIC_LIB = True
+STATIC_LIBRARY_NAME = 'js_static'
+
+if CONFIG['ENABLE_INTL_API']:
+    if not CONFIG['MOZ_ICU_DATA_ARCHIVE']:
+        USE_LIBS += [
+            'icu',
+        ]
+    else:
+        # Linking 'icu' will pull in the stubdata library,
+        # which the shell doesn't want, so link the other bits.
+        USE_LIBS += [
+            'icui18n',
+            'icuuc',
+        ]
+
+USE_LIBS += [
+    'nspr',
+    'zlib',
+]
+
+if CONFIG['OS_ARCH'] not in ('WINNT', 'HP-UX'):
+    OS_LIBS += [
+        'm',
+    ]
+
+if CONFIG['OS_ARCH'] == 'FreeBSD':
+    OS_LIBS += [
+        '-pthread',
+    ]
+
+if CONFIG['OS_ARCH'] == 'Linux':
+    OS_LIBS += [
+        'dl',
+    ]
+
+if CONFIG['OS_ARCH'] == 'SunOS':
+    OS_LIBS += [
+        'posix4',
+        'dl',
+        'nsl',
+        'socket',
+    ]
+
+OS_LIBS += CONFIG['REALTIME_LIBS']
+
+NO_EXPAND_LIBS = True
+
+DIST_INSTALL = True

rename from js/src/symverscript.in
rename to js/src/build/symverscript.in

--- a/js/src/moz.build
+++ b/js/src/moz.build
@@ -47,26 +47,22 @@ if CONFIG['JS_BUNDLED_EDITLINE']:
 
 if not CONFIG['JS_DISABLE_SHELL']:
     DIRS += ['shell']
 
 TEST_DIRS += ['jsapi-tests', 'tests', 'gdb']
 
 CONFIGURE_SUBST_FILES += [
     'devtools/rootAnalysis/Makefile',
-    'js-config',
-    'js.pc',
 ]
 CONFIGURE_DEFINE_FILES += [
     'js-confdefs.h',
 ]
 
 if not CONFIG['JS_STANDALONE']:
-    LIBRARY_DEFINES['MOZ_HAS_MOZGLUE'] = True
-
     CONFIGURE_SUBST_FILES += [
         '../../config/autoconf-js.mk',
         '../../config/emptyvars-js.mk',
     ]
 
 CONFIGURE_DEFINE_FILES += [
     'js-config.h',
 ]
@@ -627,50 +623,21 @@ else:
 
 GENERATED_FILES += ['frontend/ReservedWordsGenerated.h']
 ReservedWordsGenerated = GENERATED_FILES['frontend/ReservedWordsGenerated.h']
 ReservedWordsGenerated.script = 'frontend/GenerateReservedWords.py'
 ReservedWordsGenerated.inputs += [
     'frontend/ReservedWords.h'
 ]
 
-# JavaScript must be built shared, even for static builds, as it is used by
-# other modules which are always built shared. Failure to do so results in
-# the js code getting copied into xpinstall and jsd as well as mozilla-bin,
-# and then the static data cells used for locking no longer work.
-#
-# In fact, we now build both a static and a shared library, as the
-# JS shell would like to link to the static library.
-
-if CONFIG['JS_SHARED_LIBRARY']:
-    GeckoSharedLibrary('js', linkage=None)
-    SHARED_LIBRARY_NAME = CONFIG['JS_LIBRARY_NAME']
-else:
-    Library('js')
-
-FORCE_STATIC_LIB = True
-STATIC_LIBRARY_NAME = 'js_static'
+DIRS += [
+    'build',
+]
 
-if CONFIG['ENABLE_INTL_API']:
-    if not CONFIG['MOZ_ICU_DATA_ARCHIVE']:
-        USE_LIBS += [
-            'icu',
-        ]
-    else:
-        # Linking 'icu' will pull in the stubdata library,
-        # which the shell doesn't want, so link the other bits.
-        USE_LIBS += [
-            'icui18n',
-            'icuuc',
-        ]
-
-USE_LIBS += [
-    'nspr',
-    'zlib',
-]
+FINAL_LIBRARY = 'js'
 
 if CONFIG['NIGHTLY_BUILD']:
     DEFINES['ENABLE_BINARYDATA'] = True
 
 if CONFIG['NIGHTLY_BUILD']:
     DEFINES['ENABLE_SIMD'] = True
 
 # Also set in shell/moz.build
@@ -707,48 +674,19 @@ if CONFIG['_MSC_VER']:
     CXXFLAGS += ['-wd4146'] # FIXME: unary minus operator applied to unsigned type (bug 1229189)
 
     # This is intended as a temporary hack to support building with VS2015.
     # 'noexcept' used with no exception handling mode specified;
     # termination on exception is not guaranteed. Specify /EHsc
     CXXFLAGS += ['-wd4577']
     CXXFLAGS += ['-wd4312']
 
-if CONFIG['OS_ARCH'] not in ('WINNT', 'HP-UX'):
-    OS_LIBS += [
-        'm',
-    ]
-
-if CONFIG['OS_ARCH'] == 'FreeBSD':
-    OS_LIBS += [
-        '-pthread',
-    ]
-
-if CONFIG['OS_ARCH'] == 'Linux':
-    OS_LIBS += [
-        'dl',
-    ]
-
-if CONFIG['OS_ARCH'] == 'SunOS':
-    OS_LIBS += [
-        'posix4',
-        'dl',
-        'nsl',
-        'socket',
-    ]
-
-OS_LIBS += CONFIG['REALTIME_LIBS']
-
 CFLAGS += CONFIG['MOZ_ICU_CFLAGS']
 CXXFLAGS += CONFIG['MOZ_ICU_CFLAGS']
 
-NO_EXPAND_LIBS = True
-
-DIST_INSTALL = True
-
 # Prepare self-hosted JS code for embedding
 GENERATED_FILES += [('selfhosted.out.h', 'selfhosted.js')]
 selfhosted = GENERATED_FILES[('selfhosted.out.h', 'selfhosted.js')]
 selfhosted.script = 'builtin/embedjs.py:generate_selfhosted'
 selfhosted.inputs = [
     'js.msg',
     'builtin/TypedObjectConstants.h',
     'builtin/SelfHostingDefines.h',

--- a/moz.build
+++ b/moz.build
@@ -90,43 +90,44 @@ if not CONFIG['JS_STANDALONE']:
     GENERATED_FILES['buildid.h'].script = 'build/variables.py:buildid_header'
     GENERATED_FILES['source-repo.h'].script = 'build/variables.py:source_repo_header'
 
     DIRS += [
         'build',
         'probes',
     ]
 
+if CONFIG['COMPILE_ENVIRONMENT']:
+    DIRS += ['js/src']
+
 DIRS += [
     'config/external/fdlibm',
     'config/external/nspr',
     'config/external/zlib',
     'memory',
     'mfbt',
     'mozglue',
 ]
 
 if not CONFIG['JS_STANDALONE']:
     DIRS += ['xpcom/xpidl']
 
 if CONFIG['USE_ICU']:
     DIRS += ['config/external/icu']
 
 if CONFIG['COMPILE_ENVIRONMENT']:
-
     if not CONFIG['JS_STANDALONE']:
         DIRS += [
             'config/external',
             'security',
         ]
 
     if CONFIG['BUILD_CTYPES']:
         DIRS += ['config/external/ffi']
 
-    DIRS += ['js/src']
 else:
     TEST_DIRS += ['js/src/tests']
 
 if not CONFIG['JS_STANDALONE'] and CONFIG['MOZ_BUILD_APP']:
     # Bring in the configuration for the configured application.
     include('/' + CONFIG['MOZ_BUILD_APP'] + '/app.mozbuild')
 
 CONFIGURE_SUBST_FILES += ['.cargo/config']