Bug 1951772 - Disable Mutation Events in Nightly, r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D240375

dom/tests/mochitest/general/test_interfaces.js

@@ -905,7 +905,7 @@ let interfaceNamesInGlobalScope = [
   // IMPORTANT: Do not change this list without review from a DOM peer!
   { name: "MouseScrollEvent", insecureContext: true },
   // IMPORTANT: Do not change this list without review from a DOM peer!
-  { name: "MutationEvent", insecureContext: true },
+  { name: "MutationEvent", insecureContext: true, nightly: false },
   // IMPORTANT: Do not change this list without review from a DOM peer!
   { name: "MutationObserver", insecureContext: true },
   // IMPORTANT: Do not change this list without review from a DOM peer!

dom/webidl/MutationEvent.webidl

@@ -9,7 +9,7 @@
  * Copyright © 2012 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C
  * liability, trademark and document use rules apply.
  */
-[Exposed=Window]
+[Exposed=Window, Pref="dom.mutation_events.enabled"]
 interface MutationEvent : Event
 {
   const unsigned short MODIFICATION = 1;

js/xpconnect/tests/mochitest/test_bug790732.html

@@ -29,7 +29,9 @@ async function doTest() {
   is(Ci.nsIDOMKeyEvent, KeyEvent);
   is(Ci.nsIDOMMouseEvent, MouseEvent);
   is(Ci.nsIDOMMouseScrollEvent, MouseScrollEvent);
-  is(Ci.nsIDOMMutationEvent, MutationEvent);
+  if (SpecialPowers.getBoolPref("dom.mutation_events.enabled")) {
+    is(Ci.nsIDOMMutationEvent, MutationEvent);
+  }
   is(Ci.nsIDOMUIEvent, UIEvent);
   is(Ci.nsIDOMHTMLMediaElement, HTMLMediaElement);
   is(Ci.nsIDOMRange, Range);

modules/libpref/init/StaticPrefList.yaml

@@ -3518,7 +3518,7 @@
 # Whether to dispatch mutation events.
 - name: dom.mutation_events.enabled
   type: bool
-  value: true
+  value: @IS_NOT_NIGHTLY_BUILD@
   mirror: always
 
 # Limit of location change caused by content scripts in a time span per

testing/web-platform/meta/dom/historical-mutation-events.html.ini

@@ -1,18 +1,2 @@
 [historical-mutation-events.html]
-  [Historical DOM features must be removed: MutationEvent]
-    expected: FAIL
-
-  [The DOMSubtreeModified mutation event must not be fired.]
-    expected: FAIL
-
-  [The DOMNodeInserted mutation event must not be fired.]
-    expected: FAIL
-
-  [The DOMNodeRemoved mutation event must not be fired.]
-    expected: FAIL
-
-  [The DOMCharacterDataModified mutation event must not be fired.]
-    expected: FAIL
-
-  [The DOMAttrModified mutation event must not be fired.]
-    expected: FAIL
+  prefs: [dom.mutation_events.enabled:false]