--- a/browser/app/Makefile.in
+++ b/browser/app/Makefile.in
@@ -98,9 +98,9 @@ ifdef MOZ_UPDATER
 	mv -f '$(dist_dest)/Contents/MacOS/updater.app/Contents/MacOS/org.mozilla.updater' '$(dist_dest)/Contents/Library/LaunchServices'
 	ln -s ../../../../Library/LaunchServices/org.mozilla.updater '$(dist_dest)/Contents/MacOS/updater.app/Contents/MacOS/org.mozilla.updater'
 endif
 	printf APPLMOZB > '$(dist_dest)/Contents/PkgInfo'
 endif
 
 .PHONY: features
 tools features::
-	$(PYTHON) -c 'import os, json; listing = {"system": sorted(os.listdir("$(DIST)/bin/browser/features"))}; print json.dumps(listing)' > $(DIST)/bin/browser/chrome/browser/content/browser/built_in_addons.json
+	$(call py_action,generate_builtin_addons,--features=browser/features browser/chrome/browser/content/browser/built_in_addons.json)

--- a/config/faster/rules.mk
+++ b/config/faster/rules.mk
@@ -107,8 +107,11 @@ endif
 
 $(TOPOBJDIR)/build/application.ini: $(TOPOBJDIR)/buildid.h $(TOPOBJDIR)/source-repo.h
 
 # The manifest of allowed system add-ons should be re-built when using
 # "build faster".
 ifeq ($(MOZ_BUILD_APP),browser/app)
 default: $(TOPOBJDIR)/browser/app/features
 endif
+ifeq ($(MOZ_BUILD_APP),mobile/android)
+default: $(TOPOBJDIR)/mobile/android/base/features
+endif

--- a/mobile/android/base/Makefile.in
+++ b/mobile/android/base/Makefile.in
@@ -76,16 +76,20 @@ update-fennec-wrappers:
 $(ABS_DIST)/fennec/$(OMNIJAR_NAME): FORCE
 	$(REPORT_BUILD)
 	$(MAKE) -C ../../../faster
 	$(MAKE) -C ../installer stage-package
 	$(MKDIR) -p $(@D)
 	rsync --update $(DIST)/fennec/$(notdir $(OMNIJAR_NAME)) $@
 	$(RM) $(DIST)/fennec/$(notdir $(OMNIJAR_NAME))
 
+.PHONY: features
+features::
+	$(call py_action,generate_builtin_addons,chrome/chrome/content/built_in_addons.json)
+
 ifndef MOZILLA_OFFICIAL
 # Targets built very early during a Gradle build.  In automation,
 # these are built before Gradle is invoked, and gradle-targets is not
 # made at all.  This is required to avoid building gradle-targets with
 # AB_CD=multi during multi-l10n builds.
 gradle-targets: $(generated_resources) $(generated_files)
 
 # Local developers update omni.ja during their builds.  There's a

new file mode 100644
--- /dev/null
+++ b/python/mozbuild/mozbuild/action/generate_builtin_addons.py
@@ -0,0 +1,46 @@
+# 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/.
+
+from __future__ import absolute_import, print_function, unicode_literals
+
+import argparse
+import json
+import os.path
+import sys
+
+import buildconfig
+
+
+def main(argv):
+    parser = argparse.ArgumentParser(
+        description='Produces a JSON manifest of built-in add-ons')
+    parser.add_argument('--features', type=str, dest='featuresdir',
+                        action='store', help=('The distribution sub-directory '
+                                              'containing feature add-ons'))
+    parser.add_argument('outputfile', help='File to write output to')
+    args = parser.parse_args(argv)
+
+    bindir = os.path.join(buildconfig.topobjdir, 'dist/bin')
+
+    def find_dictionaries(path):
+        dicts = {}
+        for filename in os.listdir(os.path.join(bindir, path)):
+            base, ext = os.path.splitext(filename)
+            if ext == '.dic':
+                dicts[base] = '%s/%s' % (path, filename)
+        return dicts
+
+    listing = {
+        "dictionaries": find_dictionaries("dictionaries"),
+    }
+    if args.featuresdir:
+        listing["system"] = sorted(os.listdir(os.path.join(bindir,
+                                                           args.featuresdir)))
+
+    with open(os.path.join(bindir, args.outputfile), 'w') as fh:
+        json.dump(listing, fh, sort_keys=True)
+
+
+if __name__ == '__main__':
+    sys.exit(main(sys.argv[1:]))