--- a/python/mozbuild/mozpack/packager/formats.py
+++ b/python/mozbuild/mozpack/packager/formats.py
@@ -18,21 +18,16 @@ from mozpack.files import (
     XPTFile,
 )
 from mozpack.copier import (
     FileRegistry,
     FileRegistrySubtree,
     Jarrer,
 )
 
-STARTUP_CACHE_PATHS = [
-    'jsloader',
-    'jssubloader',
-]
-
 '''
 Formatters are classes receiving packaging instructions and creating the
 appropriate package layout.
 
 There are three distinct formatters, each handling one of the different chrome
 formats:
     - flat: essentially, copies files from the source with the same file system
       layout. Manifests entries are grouped in a single manifest per directory,
@@ -316,9 +311,9 @@ class OmniJarSubFormatter(PiecemealForma
             return len(path) != 3 or \
                 not (path[2] == 'channel-prefs.js' and
                      path[1] in ['pref', 'preferences'])
         return path[0] in [
             'modules',
             'greprefs.js',
             'hyphenation',
             'update.locale',
-        ] or path[0] in STARTUP_CACHE_PATHS
+        ]

--- a/python/mozbuild/mozpack/packager/unpack.py
+++ b/python/mozbuild/mozpack/packager/unpack.py
@@ -18,20 +18,17 @@ from mozpack.chrome.manifest import (
     is_manifest,
 )
 from mozpack.mozjar import JarReader
 from mozpack.copier import (
     FileRegistry,
     FileCopier,
 )
 from mozpack.packager import SimplePackager
-from mozpack.packager.formats import (
-    FlatFormatter,
-    STARTUP_CACHE_PATHS,
-)
+from mozpack.packager.formats import FlatFormatter
 from urlparse import urlparse
 
 
 class UnpackFinder(BaseFinder):
     '''
     Special Finder object that treats the source package directory as if it
     were in the flat chrome format, whatever chrome format it actually is in.
 
@@ -183,18 +180,17 @@ def unpack_to_registry(source, registry)
     '''
     Transform a jar chrome or omnijar packaged directory into a flat package.
 
     The given registry is filled with the flat package.
     '''
     finder = UnpackFinder(source)
     packager = SimplePackager(FlatFormatter(registry))
     for p, f in finder.find('*'):
-        if mozpath.split(p)[0] not in STARTUP_CACHE_PATHS:
-            packager.add(p, f)
+        packager.add(p, f)
     packager.close()
 
 
 def unpack(source):
     '''
     Transform a jar chrome or omnijar packaged directory into a flat package.
     '''
     copier = FileCopier()

--- a/python/mozbuild/mozpack/test/test_packager_formats.py
+++ b/python/mozbuild/mozpack/test/test_packager_formats.py
@@ -403,18 +403,16 @@ class TestFormatters(unittest.TestCase):
             self.assertTrue(
                 is_resource(base, 'defaults/preferences/foo.js'))
             self.assertFalse(
                 is_resource(base, 'defaults/preferences/channel-prefs.js'))
             self.assertTrue(is_resource(base, 'modules/foo.jsm'))
             self.assertTrue(is_resource(base, 'greprefs.js'))
             self.assertTrue(is_resource(base, 'hyphenation/foo'))
             self.assertTrue(is_resource(base, 'update.locale'))
-            self.assertTrue(
-                is_resource(base, 'jsloader/resource/gre/modules/foo.jsm'))
             self.assertFalse(is_resource(base, 'foo'))
             self.assertFalse(is_resource(base, 'foo/bar/greprefs.js'))
             self.assertTrue(is_resource(base, 'defaults/messenger/foo.dat'))
             self.assertFalse(
                 is_resource(base, 'defaults/messenger/mailViews.dat'))
             self.assertTrue(is_resource(base, 'defaults/pref/foo.js'))
             self.assertFalse(is_resource(base, 'defaults/foo/bar.dat'))
             self.assertFalse(is_resource(base, 'defaults/foo/bar/baz.dat'))

--- a/toolkit/mozapps/installer/packager.py
+++ b/toolkit/mozapps/installer/packager.py
@@ -24,17 +24,16 @@ from mozpack.copier import (
 )
 from mozpack.errors import errors
 import mozpack.path as mozpath
 import buildconfig
 from argparse import ArgumentParser
 import os
 from StringIO import StringIO
 import subprocess
-import platform
 import mozinfo
 
 # List of libraries to shlibsign.
 SIGN_LIBS = [
     'softokn3',
     'nssdbm3',
     'freebl3',
     'freeblpriv3',
@@ -119,70 +118,16 @@ class LibSignFile(File):
         if os.path.exists(dest) and skip_if_older and \
                 int(os.path.getmtime(self.path) * 1000) <= \
                 int(os.path.getmtime(dest) * 1000):
             return False
         if launcher.launch(['shlibsign', '-v', '-o', dest, '-i', self.path]):
             errors.fatal('Error while signing %s' % self.path)
 
 
-def precompile_cache(registry, source_path, gre_path, app_path):
-    '''
-    Create startup cache for the given application directory, using the
-    given GRE path.
-    - registry is a FileRegistry-like instance where to add the startup cache.
-    - source_path is the base path of the package.
-    - gre_path is the GRE path, relative to source_path.
-    - app_path is the application path, relative to source_path.
-    Startup cache for all resources under resource://app/ are generated,
-    except when gre_path == app_path, in which case it's under
-    resource://gre/.
-    '''
-    from tempfile import mkstemp
-    source_path = os.path.abspath(source_path)
-    if app_path != gre_path:
-        resource = 'app'
-    else:
-        resource = 'gre'
-    app_path = os.path.join(source_path, app_path)
-    gre_path = os.path.join(source_path, gre_path)
-
-    fd, cache = mkstemp('.zip')
-    os.close(fd)
-    os.remove(cache)
-
-    try:
-        extra_env = {'MOZ_STARTUP_CACHE': cache}
-        if buildconfig.substs.get('MOZ_TSAN'):
-            extra_env['TSAN_OPTIONS'] = 'report_bugs=0'
-        if buildconfig.substs.get('MOZ_ASAN'):
-            extra_env['ASAN_OPTIONS'] = 'detect_leaks=0'
-        if launcher.launch(['xpcshell', '-g', gre_path, '-a', app_path,
-                            '-f', os.path.join(os.path.dirname(__file__),
-                            'precompile_cache.js'),
-                            '-e', 'precompile_startupcache("resource://%s/");'
-                                  % resource],
-                           extra_linker_path=gre_path,
-                           extra_env=extra_env):
-            errors.fatal('Error while running startup cache precompilation')
-            return
-        from mozpack.mozjar import JarReader
-        jar = JarReader(cache)
-        resource = '/resource/%s/' % resource
-        for f in jar:
-            if resource in f.filename:
-                path = f.filename[f.filename.index(resource) + len(resource):]
-                if registry.contains(path):
-                    registry.add(f.filename, GeneratedFile(f.read()))
-        jar.close()
-    finally:
-        if os.path.exists(cache):
-            os.remove(cache)
-
-
 class RemovedFiles(GeneratedFile):
     '''
     File class for removed-files. Is used as a preprocessor parser.
     '''
     def __init__(self, copier):
         self.copier = copier
         GeneratedFile.__init__(self, '')
 
@@ -366,32 +311,13 @@ def main():
         log = JarLog(args.jarlog)
         for p, f in copier:
             if not isinstance(f, Jarrer):
                 continue
             key = JarLog.canonicalize(os.path.join(args.destination, p))
             if key in log:
                 f.preload(log[key])
 
-    # Fill startup cache
-    if isinstance(formatter, OmniJarFormatter) and launcher.can_launch() \
-      and buildconfig.substs['MOZ_DISABLE_STARTUPCACHE'] != '1':
-        gre_path = None
-        def get_bases():
-            for b in sink.packager.get_bases(addons=False):
-                for p in (mozpath.join('bin', b), b):
-                    if os.path.exists(os.path.join(args.source, p)):
-                        yield p
-                        break
-        for base in sorted(get_bases()):
-            if not gre_path:
-                gre_path = base
-            omnijar_path = mozpath.join(sink.normalize_path(base),
-                                        buildconfig.substs['OMNIJAR_NAME'])
-            if formatter.contains(omnijar_path):
-                precompile_cache(formatter.copier[omnijar_path],
-                                 args.source, gre_path, base)
-
     copier.copy(args.destination)
 
 
 if __name__ == '__main__':
     main()