--- a/layout/style/nsAnimationManager.cpp
+++ b/layout/style/nsAnimationManager.cpp
@@ -880,76 +880,46 @@ GeckoCSSAnimationBuilder::GetKeyframePro
 
     result.AppendElement(Move(pair));
     aAnimatedProperties.AddProperty(prop);
   }
 
   return result;
 }
 
-// Utility function to walk through |aIter| to find the Keyframe with
-// matching offset and timing function but stopping as soon as the offset
-// differs from |aOffset| (i.e. it assumes a sorted iterator).
-//
-// If a matching Keyframe is found,
-//   Returns true and sets |aIndex| to the index of the matching Keyframe
-//   within |aIter|.
-//
-// If no matching Keyframe is found,
-//   Returns false and sets |aIndex| to the index in the iterator of the
-//   first Keyframe with an offset differing to |aOffset| or, if the end
-//   of the iterator is reached, sets |aIndex| to the index after the last
-//   Keyframe.
-template <class IterType>
-static bool
-FindMatchingKeyframe(
-    IterType&& aIter,
-    double aOffset,
-    const Maybe<ComputedTimingFunction>& aTimingFunctionToMatch,
-    size_t& aIndex)
-{
-  aIndex = 0;
-  for (Keyframe& keyframe : aIter) {
-    if (keyframe.mOffset.value() != aOffset) {
-      break;
-    }
-    if (keyframe.mTimingFunction == aTimingFunctionToMatch) {
-      return true;
-    }
-    ++aIndex;
-  }
-  return false;
-}
-
 void
 GeckoCSSAnimationBuilder::FillInMissingKeyframeValues(
     nsCSSPropertyIDSet aAnimatedProperties,
     nsCSSPropertyIDSet aPropertiesSetAtStart,
     nsCSSPropertyIDSet aPropertiesSetAtEnd,
     const Maybe<ComputedTimingFunction>& aInheritedTimingFunction,
     nsTArray<Keyframe>& aKeyframes)
 {
   static const size_t kNotSet = static_cast<size_t>(-1);
 
   // Find/create the keyframe to add start values to
   size_t startKeyframeIndex = kNotSet;
   if (!aAnimatedProperties.Equals(aPropertiesSetAtStart) &&
-      !FindMatchingKeyframe(aKeyframes, 0.0, aInheritedTimingFunction,
-                            startKeyframeIndex)) {
+      !nsAnimationManager::FindMatchingKeyframe(aKeyframes,
+                                                0.0,
+                                                aInheritedTimingFunction,
+                                                startKeyframeIndex)) {
     Keyframe newKeyframe;
     newKeyframe.mOffset.emplace(0.0);
     newKeyframe.mTimingFunction = aInheritedTimingFunction;
     aKeyframes.InsertElementAt(startKeyframeIndex, Move(newKeyframe));
   }
 
   // Find/create the keyframe to add end values to
   size_t endKeyframeIndex = kNotSet;
   if (!aAnimatedProperties.Equals(aPropertiesSetAtEnd)) {
-    if (!FindMatchingKeyframe(Reversed(aKeyframes), 1.0,
-                              aInheritedTimingFunction, endKeyframeIndex)) {
+    if (!nsAnimationManager::FindMatchingKeyframe(Reversed(aKeyframes),
+                                                  1.0,
+                                                  aInheritedTimingFunction,
+                                                  endKeyframeIndex)) {
       Keyframe newKeyframe;
       newKeyframe.mOffset.emplace(1.0);
       newKeyframe.mTimingFunction = aInheritedTimingFunction;
       aKeyframes.AppendElement(Move(newKeyframe));
       endKeyframeIndex = aKeyframes.Length() - 1;
     } else {
       // endKeyframeIndex is currently a count from the end of the array
       // so we need to reverse it.

--- a/layout/style/nsAnimationManager.h
+++ b/layout/style/nsAnimationManager.h
@@ -5,16 +5,17 @@
 #ifndef nsAnimationManager_h_
 #define nsAnimationManager_h_
 
 #include "mozilla/Attributes.h"
 #include "mozilla/ContentEvents.h"
 #include "mozilla/EventForwards.h"
 #include "AnimationCommon.h"
 #include "mozilla/dom/Animation.h"
+#include "mozilla/Keyframe.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/TimeStamp.h"
 
 class nsIGlobalObject;
 class nsStyleContext;
 struct nsStyleDisplay;
 struct ServoComputedValues;
 
@@ -352,16 +353,49 @@ public:
   void DispatchEvents()
   {
     RefPtr<nsAnimationManager> kungFuDeathGrip(this);
     mEventDispatcher.DispatchEvents(mPresContext);
   }
   void SortEvents()      { mEventDispatcher.SortEvents(); }
   void ClearEventQueue() { mEventDispatcher.ClearEventQueue(); }
 
+  // Utility function to walk through |aIter| to find the Keyframe with
+  // matching offset and timing function but stopping as soon as the offset
+  // differs from |aOffset| (i.e. it assumes a sorted iterator).
+  //
+  // If a matching Keyframe is found,
+  //   Returns true and sets |aIndex| to the index of the matching Keyframe
+  //   within |aIter|.
+  //
+  // If no matching Keyframe is found,
+  //   Returns false and sets |aIndex| to the index in the iterator of the
+  //   first Keyframe with an offset differing to |aOffset| or, if the end
+  //   of the iterator is reached, sets |aIndex| to the index after the last
+  //   Keyframe.
+  template <class IterType, class TimingFunctionType>
+  static bool FindMatchingKeyframe(
+    IterType&& aIter,
+    double aOffset,
+    const TimingFunctionType& aTimingFunctionToMatch,
+    size_t& aIndex)
+  {
+    aIndex = 0;
+    for (mozilla::Keyframe& keyframe : aIter) {
+      if (keyframe.mOffset.value() != aOffset) {
+        break;
+      }
+      if (keyframe.mTimingFunction == aTimingFunctionToMatch) {
+        return true;
+      }
+      ++aIndex;
+    }
+    return false;
+  }
+
 protected:
   ~nsAnimationManager() override = default;
 
 private:
   template<class BuilderType>
   void DoUpdateAnimations(
     const mozilla::NonOwningAnimationTarget& aTarget,
     const nsStyleDisplay& aStyleDisplay,