diff --git a/python/mozbuild/mozbuild/backend/recursivemake.py b/python/mozbuild/mozbuild/backend/recursivemake.py
index 5bca4df0afca..dc8b488312c7 100644
--- a/python/mozbuild/mozbuild/backend/recursivemake.py
+++ b/python/mozbuild/mozbuild/backend/recursivemake.py
@@ -57,6 +57,7 @@ from ..frontend.data import (
     InstallationTarget,
     JARManifest,
     JavaJarData,
+    JavaScriptModules,
     Library,
     LocalInclude,
     PerSourceFlag,
@@ -561,6 +562,9 @@ class RecursiveMakeBackend(CommonBackend):
         elif isinstance(obj, InstallationTarget):
             self._process_installation_target(obj, backend_file)
 
+        elif isinstance(obj, JavaScriptModules):
+            self._process_javascript_modules(obj, backend_file)
+
         elif isinstance(obj, ContextWrapped):
             # Process a rich build system object from the front-end
             # as-is.  Please follow precedent and handle CamelCaseData
@@ -1023,6 +1027,18 @@ INSTALL_TARGETS += %(prefix)s
         if not obj.enabled:
             backend_file.write('NO_DIST_INSTALL := 1\n')
 
+    def _process_javascript_modules(self, obj, backend_file):
+        if obj.flavor != 'testing':
+            raise Exception('Unsupported JavaScriptModules instance: %s' % obj.flavor)
+
+        if not self.environment.substs.get('ENABLE_TESTS', False):
+            return
+
+        manifest = self._install_manifests['tests']
+
+        for source, dest, _ in self._walk_hierarchy(obj, obj.modules):
+            manifest.add_symlink(source, mozpath.join('modules', dest))
+
     def _handle_idl_manager(self, manager):
         build_files = self._install_manifests['xpidl']
 
diff --git a/python/mozbuild/mozbuild/frontend/context.py b/python/mozbuild/mozbuild/frontend/context.py
index 4d9e3ce2f8e1..06827ec2a749 100644
--- a/python/mozbuild/mozbuild/frontend/context.py
+++ b/python/mozbuild/mozbuild/frontend/context.py
@@ -1001,10 +1001,16 @@ VARIABLES = {
         """Like ``FINAL_TARGET_FILES``, with preprocessing.
         """, 'libs'),
 
-    'TESTING_FILES': (HierarchicalStringList, list,
-        """List of files to be installed in the _tests directory.
+    'TESTING_JS_MODULES': (HierarchicalStringList, list,
+        """JavaScript modules to install in the test-only destination.
 
-        This works similarly to FINAL_TARGET_FILES.
+        Some JavaScript modules (JSMs) are test-only and not distributed
+        with Firefox. This variable defines them.
+
+        To install modules in a subdirectory, use properties of this
+        variable to control the final destination. e.g.
+
+        ``TESTING_JS_MODULES.foo += ['module.jsm']``.
         """, None),
 
     'FINAL_LIBRARY': (unicode, unicode,
@@ -1968,18 +1974,6 @@ SPECIAL_VARIABLES = {
         ``$(FINAL_TARGET)/modules``, after preprocessing.
         """),
 
-    'TESTING_JS_MODULES': (lambda context: context['TESTING_FILES'].modules, list,
-        """JavaScript modules to install in the test-only destination.
-
-        Some JavaScript modules (JSMs) are test-only and not distributed
-        with Firefox. This variable defines them.
-
-        To install modules in a subdirectory, use properties of this
-        variable to control the final destination. e.g.
-
-        ``TESTING_JS_MODULES.foo += ['module.jsm']``.
-        """),
-
 }
 
 # Deprecation hints.
diff --git a/python/mozbuild/mozbuild/frontend/data.py b/python/mozbuild/mozbuild/frontend/data.py
index 5ba15c607b8f..782e0f40e283 100644
--- a/python/mozbuild/mozbuild/frontend/data.py
+++ b/python/mozbuild/mozbuild/frontend/data.py
@@ -652,6 +652,21 @@ class JARManifest(ContextDerived):
         self.path = path
 
 
+class JavaScriptModules(ContextDerived):
+    """Describes a JavaScript module."""
+
+    __slots__ = (
+        'modules',
+        'flavor',
+    )
+
+    def __init__(self, context, modules, flavor):
+        super(JavaScriptModules, self).__init__(context)
+
+        self.modules = modules
+        self.flavor = flavor
+
+
 class ContextWrapped(ContextDerived):
     """Generic context derived container object for a wrapped rich object.
 
@@ -826,12 +841,6 @@ class FinalTargetPreprocessedFiles(ContextDerived):
         self.files = files
 
 
-class TestingFiles(FinalTargetFiles):
-    @property
-    def install_target(self):
-        return '_tests'
-
-
 class GeneratedFile(ContextDerived):
     """Represents a generated file."""
 
diff --git a/python/mozbuild/mozbuild/frontend/emitter.py b/python/mozbuild/mozbuild/frontend/emitter.py
index 87fabc25694f..94617f4053bc 100644
--- a/python/mozbuild/mozbuild/frontend/emitter.py
+++ b/python/mozbuild/mozbuild/frontend/emitter.py
@@ -53,6 +53,7 @@ from .data import (
     InstallationTarget,
     IPDLFile,
     JARManifest,
+    JavaScriptModules,
     Library,
     Linkable,
     LinkageWrongKindError,
@@ -66,7 +67,6 @@ from .data import (
     Sources,
     StaticLibrary,
     TestHarnessFiles,
-    TestingFiles,
     TestWebIDLFile,
     TestManifest,
     UnifiedSources,
@@ -629,6 +629,10 @@ class TreeMetadataEmitter(LoggingMixin):
 
         self._handle_programs(context)
 
+        test_js_modules = context.get('TESTING_JS_MODULES')
+        if test_js_modules:
+            yield JavaScriptModules(context, test_js_modules, 'testing')
+
         simple_lists = [
             ('GENERATED_EVENTS_WEBIDL_FILES', GeneratedEventWebIDLFile),
             ('GENERATED_WEBIDL_FILES', GeneratedWebIDLFile),
@@ -655,12 +659,11 @@ class TreeMetadataEmitter(LoggingMixin):
         for var, cls in (
             ('FINAL_TARGET_FILES', FinalTargetFiles),
             ('FINAL_TARGET_PP_FILES', FinalTargetPreprocessedFiles),
-            ('TESTING_FILES', TestingFiles),
         ):
             all_files = context.get(var)
             if not all_files:
                 continue
-            if dist_install is False and var != 'TESTING_FILES':
+            if dist_install is False:
                 raise SandboxValidationError(
                     '%s cannot be used with DIST_INSTALL = False' % var,
                     context)