--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -1172,21 +1172,28 @@ class CGClassConstructor(CGAbstractStati
     def definition_body(self):
         return self.generate_code()
 
     def generate_code(self):
         preamble = """
   JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
   JS::Rooted<JSObject*> obj(cx, &args.callee());
 """
+        # [ChromeOnly] interfaces may only be constructed by chrome.
+        # Additionally, we want to throw if a non-chrome caller does a bareword invocation of a
+        # constructor without |new|. We don't enforce this for chrome to avoid the addon compat
+        # fallout of making that change. See bug 916644.
         if isChromeOnly(self._ctor):
-            preamble += """  if (!nsContentUtils::ThreadsafeIsCallerChrome()) {
+            mayInvokeCtor = "nsContentUtils::ThreadsafeIsCallerChrome()"
+        else:
+            mayInvokeCtor = "(args.isConstructing() || nsContentUtils::ThreadsafeIsCallerChrome())"
+        preamble += """  if (!%s) {
     return ThrowingConstructor(cx, argc, vp);
   }
-"""
+""" % mayInvokeCtor
         name = self._ctor.identifier.name
         nativeName = MakeNativeName(self.descriptor.binaryNames.get(name, name))
         callGenerator = CGMethodCall(nativeName, True, self.descriptor,
                                      self._ctor, isConstructor=True)
         return preamble + callGenerator.define();
 
 # Encapsulate the constructor in a helper method to share genConstructorBody with CGJSImplMethod.
 class CGConstructNavigatorObjectHelper(CGAbstractStaticMethod):

--- a/dom/tests/mochitest/bugs/test_bug370098.html
+++ b/dom/tests/mochitest/bugs/test_bug370098.html
@@ -19,20 +19,19 @@ https://bugzilla.mozilla.org/show_bug.cg
 /** Test for Bug 370098 **/
 function test_constructor(dom_proto, shouldthrow) {
     var threw = false;
     try {
         window[dom_proto]();
     } catch (e) {
         threw = true;
     }
-    if (shouldthrow)
-      ok(threw, "Calling |" + dom_proto + "()| should throw");
-    else
-      todo(threw, "Calling |" + dom_proto + "()| should throw");
+    // XSLTProcessor is still on the old bindings.
+    if (dom_proto != 'XSLTProcessor')
+      ok(threw, "Calling |" + dom_proto + "()| should always throw");
 
     threw = false;
     try {
         new window[dom_proto]();
     } catch (e) {
         threw = true;
     }
     is(threw, shouldthrow, "Calling |new " + dom_proto + "()| should" + (shouldthrow ? " " : " not ") + "throw");