2 files changed, 45 insertions, 13 deletions

diff --git a/layout/style/nsTransitionManager.cpp b/layout/style/nsTransitionManager.cpp
index da12a0ecd..abb9e2311 100644
--- a/layout/style/nsTransitionManager.cpp
+++ b/layout/style/nsTransitionManager.cpp
@@ -182,8 +182,7 @@ CSSTransition::UpdateTiming(SeekFlag aSeekFlag, SyncNotifyFlag aSyncNotifyFlag)
 void
 CSSTransition::QueueEvents(StickyTimeDuration aActiveTime)
 {
-  if (!mEffect ||
-      !mOwningElement.IsSet()) {
+  if (!mOwningElement.IsSet()) {
     return;
   }
 
@@ -197,14 +196,27 @@ CSSTransition::QueueEvents(StickyTimeDuration aActiveTime)
     return;
   }
 
-  ComputedTiming computedTiming = mEffect->GetComputedTiming();
-  const StickyTimeDuration zeroDuration;
-  StickyTimeDuration intervalStartTime =
-    std::max(std::min(StickyTimeDuration(-mEffect->SpecifiedTiming().mDelay),
-                      computedTiming.mActiveDuration), zeroDuration);
-  StickyTimeDuration intervalEndTime =
-    std::max(std::min((EffectEnd() - mEffect->SpecifiedTiming().mDelay),
-                      computedTiming.mActiveDuration), zeroDuration);
+  const StickyTimeDuration zeroDuration = StickyTimeDuration();
+
+  TransitionPhase currentPhase;
+  StickyTimeDuration intervalStartTime;
+  StickyTimeDuration intervalEndTime;
+
+  if (!mEffect) {
+    currentPhase      = GetTransitionPhaseWithoutEffect();
+    intervalStartTime = zeroDuration;
+    intervalEndTime   = zeroDuration;
+  } else {
+    ComputedTiming computedTiming = mEffect->GetComputedTiming();
+
+    currentPhase = static_cast<TransitionPhase>(computedTiming.mPhase);
+    intervalStartTime =
+      std::max(std::min(StickyTimeDuration(-mEffect->SpecifiedTiming().mDelay),
+                        computedTiming.mActiveDuration), zeroDuration);
+    intervalEndTime =
+      std::max(std::min((EffectEnd() - mEffect->SpecifiedTiming().mDelay),
+                        computedTiming.mActiveDuration), zeroDuration);
+  }
 
   // TimeStamps to use for ordering the events when they are dispatched. We
   // use a TimeStamp so we can compare events produced by different elements,
@@ -215,14 +227,11 @@ CSSTransition::QueueEvents(StickyTimeDuration aActiveTime)
   TimeStamp startTimeStamp  = ElapsedTimeToTimeStamp(intervalStartTime);
   TimeStamp endTimeStamp    = ElapsedTimeToTimeStamp(intervalEndTime);
 
-  TransitionPhase currentPhase;
   if (mPendingState != PendingState::NotPending &&
       (mPreviousTransitionPhase == TransitionPhase::Idle ||
        mPreviousTransitionPhase == TransitionPhase::Pending))
   {
     currentPhase = TransitionPhase::Pending;
-  } else {
-    currentPhase = static_cast<TransitionPhase>(computedTiming.mPhase);
   }
 
   AutoTArray<TransitionEventParams, 3> events;
@@ -320,6 +329,23 @@ CSSTransition::QueueEvents(StickyTimeDuration aActiveTime)
   }
 }
 
+CSSTransition::TransitionPhase
+CSSTransition::GetTransitionPhaseWithoutEffect() const
+{
+  MOZ_ASSERT(!mEffect, "Should only be called when we do not have an effect");
+
+  Nullable<TimeDuration> currentTime = GetCurrentTime();
+  if (currentTime.IsNull()) {
+    return TransitionPhase::Idle;
+  }
+
+  // If we don't have a target effect, the duration will be zero so the phase is
+  // 'before' if the current time is less than zero.
+  return currentTime.Value() < TimeDuration()
+         ? TransitionPhase::Before
+         : TransitionPhase::After;
+}
+
 void
 CSSTransition::Tick()
 {
diff --git a/layout/style/nsTransitionManager.h b/layout/style/nsTransitionManager.h
index 80042adcd..e2f198a40 100644
--- a/layout/style/nsTransitionManager.h
+++ b/layout/style/nsTransitionManager.h
@@ -243,6 +243,12 @@ protected:
 
   void QueueEvents(StickyTimeDuration activeTime = StickyTimeDuration());
 
+
+  enum class TransitionPhase;
+  // Return the TransitionPhase to use when the transition doesn't have a target
+  // effect.
+  TransitionPhase GetTransitionPhaseWithoutEffect() const;
+
   // The (pseudo-)element whose computed transition-property refers to this
   // transition (if any).
   //