import changes from `dev' branch of rmottola/Arctic-Fox:

- Bug 1003204: Removed CommonUtils.exceptionStr() in toolkit/ r=gfritzsche (d1c2efa08f)
- Bug 1243936 - Convert remaining callsites within devtools/ and toolkit/ to use channel.open2() (54f398eb47)
- Bug 1187270 - Add Telemetry session ID to crash annotations, r=gfritzsche (6c08170c5a)
- Bug 1249219 - Part 4: Use NonOwningAnimationTarget as the returned value of some animation target getters. r=birtles (df788abe39)
- Bug 1249219 - Part 5: Add a wrapper of AnimationAdded/Changed/Removed. r=birtles (58cf3a3ce2)
- Bug 1249219 - Part 6: Support pseudo elements in Animation Mutation Observer. r=heycam (d10c901821)
- Bug 1249219 - Part 7: Test. r=birtles (e2b78422be)
- add back some utils of Bug 751291  used in tests (8fd2cc847f)
- Bug 1253470 - Part 1: Produce console warnings for invalid duration. r=birtles (a0491eeab4)
- Bug 1253470 - Part 2: Produce console warnings for invalid iterationStart. r=birtles (6a910650c9)
- Bug 1253470 - Part 3: Produce console warnings for invalid iterations. r=birtles (e3210e754e)
- Bug 1253470 - Part 4: Produce console warnings for invalid easing. r=birtles (fc1868b3c0)
- Bug 1245748 - Move ComputedTiming to a separate file; r=heycam (22a76e4f03)
- Bug 1245748 - Rename Keyframe-related IDL types to match changes to Web Animations spec; r=heycam, r=bz (e79338bafd)
- Bug 1245748 - Update handling of 'composite' dictionary members to match changes to the spec; r=heycam, r=bz (d9cc71cde8)
- Bug 1245748 - Define the Keyframe type for storing specified keyframes; r=heycam (a429e2bf46)
- Bug 1245748 - Add missing includes to TimingParams.{cpp,h}; r=heycam (3e1e121c6f)
- Bug 1245748 - Move keyframe handling code to a separate KeyframeUtils class; r=heycam (e359f26244)
- Bug 1245748 - Add KeyframeUtils::GetKeyframesFromObject; r=heycam (eda69445d7)
- Bug 1245748 - Add nsStyleContext parameter to StyleAnimationValue::ComputeValue(s); r=heycam (2c22b9926c)
- Bug 1245748 - Add a variant of StyleAnimationValue::ComputeValues that takes an nsCSSValue; r=heycam (12386559dd)
- Bug 1245748 - Split PropertyPriorityComparator into a separate (reusable) class; r=heycam (132394bf45)
- Bug 1245748 - Add PropertyPriorityIterator; r=heycam (bfef46fd12)
- Bug 1245748 - Add GetAnimationPropertiesFromKeyframes; r=heycam (4681ac8407)
- Bug 1245748 - Add ApplyDistributeSpacing for Keyframe objects; r=heycam (9c0bc885c9)
- Bug 1245748 - Use Keyframe-based utility functions when constructing KeyframeEffect(ReadOnly); r=heycam (e0b7460548)
- Bug 1229859 - Introduce new import-globals-from eslint rule to import globals from other modules; r=Mossop (10075a136c)

dom/base/nsDOMMutationObserver.cpp

@@ -388,31 +388,33 @@ nsAnimationReceiver::RecordAnimationMutation(Animation* aAnimation,
     return;
   }
 
-  mozilla::dom::Element* animationTarget;
-  CSSPseudoElementType pseudoType;
-  effect->GetTarget(animationTarget, pseudoType);
+  Maybe<NonOwningAnimationTarget> animationTarget = effect->GetTarget();
   if (!animationTarget) {
     return;
   }
 
-  if (!Animations() || !(Subtree() || animationTarget == Target()) ||
-      animationTarget->ChromeOnlyAccess()) {
+  dom::Element* elem = animationTarget->mElement;
+  if (!Animations() || !(Subtree() || elem == Target()) ||
+      elem->ChromeOnlyAccess()) {
+    return;
+  }
+
+  // Record animations targeting to a pseudo element only when subtree is true.
+  if (animationTarget->mPseudoType != CSSPseudoElementType::NotPseudo &&
+      !Subtree()) {
     return;
   }
 
   if (nsAutoAnimationMutationBatch::IsBatching()) {
     switch (aMutationType) {
       case eAnimationMutation_Added:
-        nsAutoAnimationMutationBatch::AnimationAdded(aAnimation,
-                                                     animationTarget);
+        nsAutoAnimationMutationBatch::AnimationAdded(aAnimation, elem);
         break;
       case eAnimationMutation_Changed:
-        nsAutoAnimationMutationBatch::AnimationChanged(aAnimation,
-                                                       animationTarget);
+        nsAutoAnimationMutationBatch::AnimationChanged(aAnimation, elem);
         break;
       case eAnimationMutation_Removed:
-        nsAutoAnimationMutationBatch::AnimationRemoved(aAnimation,
-                                                       animationTarget);
+        nsAutoAnimationMutationBatch::AnimationRemoved(aAnimation, elem);
         break;
     }
 
@@ -425,7 +427,7 @@ nsAnimationReceiver::RecordAnimationMutation(Animation* aAnimation,
 
   NS_ASSERTION(!m->mTarget, "Wrong target!");
 
-  m->mTarget = animationTarget;
+  m->mTarget = elem;
 
   switch (aMutationType) {
     case eAnimationMutation_Added: