--- a/python/mozbuild/mozbuild/backend/recursivemake.py
+++ b/python/mozbuild/mozbuild/backend/recursivemake.py
@@ -15,24 +15,28 @@ from mozpack.manifests import (
     PurgeManifest,
 )
 import mozpack.path as mozpath
 
 from .common import CommonBackend
 from ..frontend.data import (
     ConfigFileSubstitution,
     DirectoryTraversal,
+    Exports,
+    GeneratedWebIDLFile,
     IPDLFile,
     LocalInclude,
+    PreprocessedWebIDLFile,
+    Program,
     SandboxDerived,
+    TestWebIDLFile,
     VariablePassthru,
-    Exports,
-    Program,
     XPIDLFile,
     XpcshellManifests,
+    WebIDLFile,
 )
 from ..util import FileAvoidWrite
 
 
 class BackendMakeFile(object):
     """Represents a generated backend.mk file.
 
     This is both a wrapper around a file handle as well as a container that
@@ -117,16 +121,20 @@ class RecursiveMakeBackend(CommonBackend
     recursive make and thus will need this backend.
     """
 
     def _init(self):
         CommonBackend._init(self)
 
         self._backend_files = {}
         self._ipdl_sources = set()
+        self._webidl_sources = set()
+        self._test_webidl_sources = set()
+        self._preprocessed_webidl_sources = set()
+        self._generated_webidl_sources = set()
 
         def detailed(summary):
             return '{:d} total backend files. {:d} created; {:d} updated; {:d} unchanged'.format(
                 summary.managed_count, summary.created_count,
                 summary.updated_count, summary.unchanged_count)
 
         # This is a little kludgy and could be improved with a better API.
         self.summary.backend_detailed_summary = types.MethodType(detailed,
@@ -194,16 +202,31 @@ class RecursiveMakeBackend(CommonBackend
                 else:
                     backend_file.write('%s := %s\n' % (k, v))
         elif isinstance(obj, Exports):
             self._process_exports(obj, obj.exports, backend_file)
 
         elif isinstance(obj, IPDLFile):
             self._ipdl_sources.add(mozpath.join(obj.srcdir, obj.basename))
 
+        elif isinstance(obj, WebIDLFile):
+            self._webidl_sources.add(mozpath.join(obj.srcdir, obj.basename))
+
+        elif isinstance(obj, TestWebIDLFile):
+            self._test_webidl_sources.add(mozpath.join(obj.srcdir,
+                                                       obj.basename))
+
+        elif isinstance(obj, GeneratedWebIDLFile):
+            self._generated_webidl_sources.add(mozpath.join(obj.srcdir,
+                                                            obj.basename))
+
+        elif isinstance(obj, PreprocessedWebIDLFile):
+            self._preprocessed_webidl_sources.add(mozpath.join(obj.srcdir,
+                                                               obj.basename))
+
         elif isinstance(obj, Program):
             self._process_program(obj.program, backend_file)
 
         elif isinstance(obj, XpcshellManifests):
             self._process_xpcshell_manifests(obj, backend_file)
 
         elif isinstance(obj, LocalInclude):
             self._process_local_include(obj.path, backend_file)
@@ -267,16 +290,32 @@ class RecursiveMakeBackend(CommonBackend
                 ipdls.write('CPPSRCS += %sParent.cpp\n' % root)
 
         ipdls.write('IPDLDIRS := %s\n' % ' '.join(sorted(set(os.path.dirname(p)
             for p in self._ipdl_sources))))
 
         self._update_from_avoid_write(ipdls.close())
         self.summary.managed_count += 1
 
+        # Write out master lists of WebIDL source files.
+        webidls = FileAvoidWrite(os.path.join(self.environment.topobjdir,
+              'dom', 'bindings', 'webidlsrcs.mk'))
+
+        for webidl in sorted(self._webidl_sources):
+            webidls.write('webidl_files += %s\n' % os.path.basename(webidl))
+        for webidl in sorted(self._test_webidl_sources):
+            webidls.write('test_webidl_files += %s\n' % os.path.basename(webidl))
+        for webidl in sorted(self._generated_webidl_sources):
+            webidls.write('generated_webidl_files += %s\n' % os.path.basename(webidl))
+        for webidl in sorted(self._preprocessed_webidl_sources):
+            webidls.write('preprocessed_webidl_files += %s\n' % os.path.basename(webidl))
+
+        self._update_from_avoid_write(webidls.close())
+        self.summary.managed_count += 1
+
         # Write out a dependency file used to determine whether a config.status
         # re-run is needed.
         backend_built_path = os.path.join(self.environment.topobjdir,
             'backend.%s.built' % self.__class__.__name__).replace(os.sep, '/')
         backend_deps = FileAvoidWrite('%s.pp' % backend_built_path)
         inputs = sorted(p.replace(os.sep, '/') for p in self.backend_input_files)
 
         # We need to use $(DEPTH) so the target here matches what's in