diff --git a/dom/animation/Animation.cpp b/dom/animation/Animation.cpp
index 2c85b5c7cf561..0bb6fe0acd512 100644
--- a/dom/animation/Animation.cpp
+++ b/dom/animation/Animation.cpp
@@ -255,6 +255,11 @@ void Animation::SetTimelineNoUpdate(AnimationTimeline* aTimeline) {
   }
 
   mTimeline = aTimeline;
+
+  if (mEffect) {
+    mEffect->UpdateNormalizedTiming();
+  }
+
   if (!mStartTime.IsNull()) {
     mHoldTime.SetNull();
   }
@@ -992,7 +997,7 @@ TimeStamp Animation::AnimationTimeToTimeStamp(
 TimeStamp Animation::ElapsedTimeToTimeStamp(
     const StickyTimeDuration& aElapsedTime) const {
   TimeDuration delay =
-      mEffect ? mEffect->SpecifiedTiming().Delay() : TimeDuration();
+      mEffect ? mEffect->NormalizedTiming().Delay() : TimeDuration();
   return AnimationTimeToTimeStamp(aElapsedTime + delay);
 }
 
@@ -1792,7 +1797,7 @@ StickyTimeDuration Animation::EffectEnd() const {
     return StickyTimeDuration(0);
   }
 
-  return mEffect->SpecifiedTiming().EndTime();
+  return mEffect->NormalizedTiming().EndTime();
 }
 
 Document* Animation::GetRenderedDocument() const {
@@ -1916,7 +1921,7 @@ StickyTimeDuration Animation::IntervalStartTime(
              "Should be called for CSS animations or transitions");
   static constexpr StickyTimeDuration zeroDuration = StickyTimeDuration();
   return std::max(
-      std::min(StickyTimeDuration(-mEffect->SpecifiedTiming().Delay()),
+      std::min(StickyTimeDuration(-mEffect->NormalizedTiming().Delay()),
                aActiveDuration),
       zeroDuration);
 }
@@ -1932,7 +1937,7 @@ StickyTimeDuration Animation::IntervalEndTime(
              "Should be called for CSS animations or transitions");
 
   static constexpr StickyTimeDuration zeroDuration = StickyTimeDuration();
-  return std::max(std::min((EffectEnd() - mEffect->SpecifiedTiming().Delay()),
+  return std::max(std::min((EffectEnd() - mEffect->NormalizedTiming().Delay()),
                            aActiveDuration),
                   zeroDuration);
 }
diff --git a/dom/animation/AnimationEffect.cpp b/dom/animation/AnimationEffect.cpp
index 3ed190121845d..17c3741898ef7 100644
--- a/dom/animation/AnimationEffect.cpp
+++ b/dom/animation/AnimationEffect.cpp
@@ -75,6 +75,8 @@ void AnimationEffect::SetSpecifiedTiming(TimingParams&& aTiming) {
 
   mTiming = aTiming;
 
+  UpdateNormalizedTiming();
+
   if (mAnimation) {
     Maybe<nsAutoAnimationMutationBatch> mb;
     if (AsKeyframeEffect() && AsKeyframeEffect()->GetAnimationTarget()) {
@@ -91,6 +93,7 @@ void AnimationEffect::SetSpecifiedTiming(TimingParams&& aTiming) {
       AsKeyframeEffect()->RequestRestyle(EffectCompositor::RestyleType::Layer);
     }
   }
+
   // For keyframe effects, NotifyEffectTimingUpdated above will eventually
   // cause KeyframeEffect::NotifyAnimationTimingUpdated to be called so it can
   // update its registration with the target element as necessary.
@@ -266,7 +269,7 @@ ComputedTiming AnimationEffect::GetComputedTiming(
     const TimingParams* aTiming) const {
   double playbackRate = mAnimation ? mAnimation->PlaybackRate() : 1;
   return GetComputedTimingAt(
-      GetLocalTime(), aTiming ? *aTiming : SpecifiedTiming(), playbackRate);
+      GetLocalTime(), aTiming ? *aTiming : NormalizedTiming(), playbackRate);
 }
 
 // Helper function for generating an (Computed)EffectTiming dictionary
@@ -333,6 +336,17 @@ void AnimationEffect::UpdateTiming(const OptionalEffectTiming& aTiming,
   SetSpecifiedTiming(std::move(timing));
 }
 
+void AnimationEffect::UpdateNormalizedTiming() {
+  mNormalizedTiming.reset();
+
+  if (!mAnimation || !mAnimation->UsingScrollTimeline()) {
+    return;
+  }
+
+  mNormalizedTiming.emplace(mTiming);
+  mNormalizedTiming->Normalize();
+}
+
 Nullable<TimeDuration> AnimationEffect::GetLocalTime() const {
   // Since the *animation* start time is currently always zero, the local
   // time is equal to the parent time.
diff --git a/dom/animation/AnimationEffect.h b/dom/animation/AnimationEffect.h
index 0986650f11834..7c71c3cb96a49 100644
--- a/dom/animation/AnimationEffect.h
+++ b/dom/animation/AnimationEffect.h
@@ -41,7 +41,7 @@ class AnimationEffect : public nsISupports, public nsWrapperCache {
   bool IsCurrent() const;
   bool IsInEffect() const;
   bool HasFiniteActiveDuration() const {
-    return SpecifiedTiming().ActiveDuration() != TimeDuration::Forever();
+    return NormalizedTiming().ActiveDuration() != TimeDuration::Forever();
   }
 
   // AnimationEffect interface
@@ -50,17 +50,23 @@ class AnimationEffect : public nsISupports, public nsWrapperCache {
   virtual void UpdateTiming(const OptionalEffectTiming& aTiming,
                             ErrorResult& aRv);
 
-  const TimingParams& SpecifiedTiming() const {
-    return mAnimation && mAnimation->UsingScrollTimeline()
-               // This returns the TimingParams which is used for getting
-               // ComputedTiming. For now, we assume all the callers of
-               // SpecifiedTiming() want to use this for scroll-timelines
-               // (and let the animation events be an undefined part).
-               ? ScrollTimeline::GetTiming()
-               : mTiming;
-  }
+  const TimingParams& SpecifiedTiming() const { return mTiming; }
   void SetSpecifiedTiming(TimingParams&& aTiming);
 
+  const TimingParams& NormalizedTiming() const {
+    MOZ_ASSERT((mAnimation && mAnimation->UsingScrollTimeline() &&
+                mNormalizedTiming) ||
+                   !mNormalizedTiming,
+               "We do normalization only for progress-based timeline");
+    return mNormalizedTiming ? *mNormalizedTiming : mTiming;
+  }
+
+  // There are 3 conditions where we have to update the normalized timing:
+  // 1. mAnimation is changed, or
+  // 2. the timeline of mAnimation is changed, or
+  // 3. mTiming is changed.
+  void UpdateNormalizedTiming();
+
   // This function takes as input the timing parameters of an animation and
   // returns the computed timing at the specified local time.
   //
@@ -98,6 +104,7 @@ class AnimationEffect : public nsISupports, public nsWrapperCache {
   RefPtr<Document> mDocument;
   RefPtr<Animation> mAnimation;
   TimingParams mTiming;
+  Maybe<TimingParams> mNormalizedTiming;
 };
 
 }  // namespace dom
diff --git a/dom/animation/CSSAnimation.h b/dom/animation/CSSAnimation.h
index 9210dfd04bd32..ce6c392146eed 100644
--- a/dom/animation/CSSAnimation.h
+++ b/dom/animation/CSSAnimation.h
@@ -158,7 +158,7 @@ class CSSAnimation final : public Animation {
   // This is used for setting the elapsedTime member of CSS AnimationEvents.
   TimeDuration InitialAdvance() const {
     return mEffect ? std::max(TimeDuration(),
-                              mEffect->SpecifiedTiming().Delay() * -1)
+                              mEffect->NormalizedTiming().Delay() * -1)
                    : TimeDuration();
   }
 
diff --git a/dom/animation/KeyframeEffect.cpp b/dom/animation/KeyframeEffect.cpp
index 245a587388498..7769a935d6b78 100644
--- a/dom/animation/KeyframeEffect.cpp
+++ b/dom/animation/KeyframeEffect.cpp
@@ -1862,6 +1862,8 @@ void KeyframeEffect::SetAnimation(Animation* aAnimation) {
 
   mAnimation = aAnimation;
 
+  UpdateNormalizedTiming();
+
   // The order of these function calls is important:
   // NotifyAnimationTimingUpdated() need the updated mIsRelevant flag to check
   // if it should create the effectSet or not, and MarkCascadeNeedsUpdate()
diff --git a/dom/animation/ScrollTimeline.cpp b/dom/animation/ScrollTimeline.cpp
index 3da0c828471fa..6c380fc482103 100644
--- a/dom/animation/ScrollTimeline.cpp
+++ b/dom/animation/ScrollTimeline.cpp
@@ -15,8 +15,6 @@
 #include "nsIScrollableFrame.h"
 #include "nsLayoutUtils.h"
 
-#define SCROLL_TIMELINE_DURATION_MILLISEC 100000
-
 namespace mozilla::dom {
 
 // ---------------------------------
@@ -43,8 +41,6 @@ NS_IMPL_CYCLE_COLLECTION_TRACE_END
 NS_IMPL_ISUPPORTS_CYCLE_COLLECTION_INHERITED_0(ScrollTimeline,
                                                AnimationTimeline)
 
-TimingParams ScrollTimeline::sTiming;
-
 ScrollTimeline::ScrollTimeline(Document* aDocument, const Scroller& aScroller,
                                StyleScrollAxis aAxis)
     : AnimationTimeline(aDocument->GetParentObject()),
@@ -52,13 +48,6 @@ ScrollTimeline::ScrollTimeline(Document* aDocument, const Scroller& aScroller,
       mSource(aScroller),
       mAxis(aAxis) {
   MOZ_ASSERT(aDocument);
-
-  // Use default values except for |mDuration| and |mFill|.
-  // Use a fixed duration defined in SCROLL_TIMELINE_DURATIONMILLISEC, and use
-  // FillMode::Both to make sure the animation is in effect at 100%.
-  sTiming = TimingParams(SCROLL_TIMELINE_DURATION_MILLISEC, 0.0,
-                         std::numeric_limits<float>::infinity(),
-                         PlaybackDirection::Alternate, FillMode::Both);
 }
 
 /* static */
@@ -222,7 +211,7 @@ Nullable<TimeDuration> ScrollTimeline::GetCurrentTimeAsDuration() const {
   // If this orientation is not ready for scrolling (i.e. the scroll range is
   // not larger than or equal to one device pixel), we make it 100%.
   if (!scrollFrame->GetAvailableScrollingDirections().contains(orientation)) {
-    return TimeDuration::FromMilliseconds(SCROLL_TIMELINE_DURATION_MILLISEC);
+    return TimeDuration::FromMilliseconds(PROGRESS_TIMELINE_DURATION_MILLISEC);
   }
 
   const nsPoint& scrollOffset = scrollFrame->GetScrollPosition();
@@ -240,7 +229,7 @@ Nullable<TimeDuration> ScrollTimeline::GetCurrentTimeAsDuration() const {
   // https://drafts.csswg.org/scroll-animations-1/#progress-calculation-algorithm
   double progress = position / range;
   return TimeDuration::FromMilliseconds(progress *
-                                        SCROLL_TIMELINE_DURATION_MILLISEC);
+                                        PROGRESS_TIMELINE_DURATION_MILLISEC);
 }
 
 layers::ScrollDirection ScrollTimeline::Axis() const {
diff --git a/dom/animation/ScrollTimeline.h b/dom/animation/ScrollTimeline.h
index b6226b77d6b08..c118462e7cdbe 100644
--- a/dom/animation/ScrollTimeline.h
+++ b/dom/animation/ScrollTimeline.h
@@ -12,7 +12,6 @@
 #include "mozilla/HashTable.h"
 #include "mozilla/PairHash.h"
 #include "mozilla/ServoStyleConsts.h"
-#include "mozilla/TimingParams.h"
 #include "mozilla/WritingModes.h"
 
 class nsIScrollableFrame;
@@ -177,8 +176,6 @@ class ScrollTimeline final : public AnimationTimeline {
 
   bool ScrollingDirectionIsAvailable() const;
 
-  static constexpr const TimingParams& GetTiming() { return sTiming; }
-
  protected:
   virtual ~ScrollTimeline() { Teardown(); }
 
@@ -208,11 +205,6 @@ class ScrollTimeline final : public AnimationTimeline {
   // nearest scroller.
   Scroller mSource;
   StyleScrollAxis mAxis;
-
-  // Note: it's unfortunate TimingParams cannot be a const variable because
-  // we have to use StickyTimingDuration::FromMilliseconds() in its
-  // constructor.
-  static TimingParams sTiming;
 };
 
 /**
diff --git a/dom/animation/TimingParams.cpp b/dom/animation/TimingParams.cpp
index 039d466438e56..be269545274b9 100644
--- a/dom/animation/TimingParams.cpp
+++ b/dom/animation/TimingParams.cpp
@@ -214,4 +214,16 @@ bool TimingParams::operator==(const TimingParams& aOther) const {
          mFunction == aOther.mFunction;
 }
 
+void TimingParams::Normalize() {
+  // FIXME: Bug 1775327, do normalization, instead of using these magic numbers.
+  mDuration = Some(StickyTimeDuration::FromMilliseconds(
+      PROGRESS_TIMELINE_DURATION_MILLISEC));
+  mDelay = TimeDuration::FromMilliseconds(0);
+  mIterations = std::numeric_limits<double>::infinity();
+  mDirection = dom::PlaybackDirection::Alternate;
+  mFill = dom::FillMode::Both;
+
+  Update();
+}
+
 }  // namespace mozilla
diff --git a/dom/animation/TimingParams.h b/dom/animation/TimingParams.h
index 2bffc17c6790c..9bf193c784859 100644
--- a/dom/animation/TimingParams.h
+++ b/dom/animation/TimingParams.h
@@ -21,6 +21,8 @@
 #include "mozilla/dom/AnimationEffectBinding.h"  // for FillMode
                                                  // and PlaybackDirection
 
+#define PROGRESS_TIMELINE_DURATION_MILLISEC 100000
+
 namespace mozilla {
 
 namespace dom {
@@ -202,6 +204,8 @@ struct TimingParams {
     return mFunction;
   }
 
+  void Normalize();
+
  private:
   void Update() {
     mActiveDuration = CalcActiveDuration(mDuration, mIterations);
diff --git a/gfx/layers/AnimationInfo.cpp b/gfx/layers/AnimationInfo.cpp
index e6e142fec0b1e..f69a54e71621e 100644
--- a/gfx/layers/AnimationInfo.cpp
+++ b/gfx/layers/AnimationInfo.cpp
@@ -427,7 +427,7 @@ void AnimationInfo::AddAnimationForProperty(
                                      ? AddAnimationForNextTransaction()
                                      : AddAnimation();
 
-  const TimingParams& timing = aAnimation->GetEffect()->SpecifiedTiming();
+  const TimingParams& timing = aAnimation->GetEffect()->NormalizedTiming();
 
   // If we are starting a new transition that replaces an existing transition
   // running on the compositor, it is possible that the animation on the
diff --git a/testing/web-platform/meta/scroll-animations/css/at-scroll-timeline-default-descriptors-iframe-print.html.ini b/testing/web-platform/meta/scroll-animations/css/at-scroll-timeline-default-descriptors-iframe-print.html.ini
new file mode 100644
index 0000000000000..652adcfd787ce
--- /dev/null
+++ b/testing/web-platform/meta/scroll-animations/css/at-scroll-timeline-default-descriptors-iframe-print.html.ini
@@ -0,0 +1,3 @@
+[at-scroll-timeline-default-descriptors-iframe-print.html]
+  expected: FAIL
+  bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1774505
diff --git a/testing/web-platform/meta/scroll-animations/css/at-scroll-timeline-default-descriptors-print.tentative.html.ini b/testing/web-platform/meta/scroll-animations/css/at-scroll-timeline-default-descriptors-print.tentative.html.ini
index 84bc531888ef3..a6c937f9e2e80 100644
--- a/testing/web-platform/meta/scroll-animations/css/at-scroll-timeline-default-descriptors-print.tentative.html.ini
+++ b/testing/web-platform/meta/scroll-animations/css/at-scroll-timeline-default-descriptors-print.tentative.html.ini
@@ -1,2 +1,4 @@
 [at-scroll-timeline-default-descriptors-print.tentative.html]
   max-asserts: 1 # Bug 1746116, an assertion to check "nextFrame || kidStatus.NextInFlowNeedsReflow()" in nsCanvasFrame::Reflow().
+  expected: FAIL
+  bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1774505
diff --git a/testing/web-platform/meta/scroll-animations/css/at-scroll-timeline-specified-scroller-print.html.ini b/testing/web-platform/meta/scroll-animations/css/at-scroll-timeline-specified-scroller-print.html.ini
index 0b807bd5ab32b..6fadc30600ae8 100644
--- a/testing/web-platform/meta/scroll-animations/css/at-scroll-timeline-specified-scroller-print.html.ini
+++ b/testing/web-platform/meta/scroll-animations/css/at-scroll-timeline-specified-scroller-print.html.ini
@@ -1,2 +1,3 @@
 [at-scroll-timeline-specified-scroller-print.html]
   expected: FAIL
+  bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1774505