diff --git a/layout/base/PresShell.cpp b/layout/base/PresShell.cpp
index cf1373b65e2b..ee9e75d8bbec 100644
--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -4462,12 +4462,6 @@ nsresult PresShell::RenderDocument(const nsRect& aRect,
   NS_ENSURE_TRUE(!(aFlags & RenderDocumentFlags::IsUntrusted),
                  NS_ERROR_NOT_IMPLEMENTED);
 
-  nsRootPresContext* rootPresContext = mPresContext->GetRootPresContext();
-  if (rootPresContext) {
-    rootPresContext->FlushWillPaintObservers();
-    if (mIsDestroying) return NS_OK;
-  }
-
   nsAutoScriptBlocker blockScripts;
 
   // Set up the rectangle as the path in aThebesContext
@@ -8837,17 +8831,6 @@ void PresShell::WillPaint() {
     return;
   }
 
-  nsRootPresContext* rootPresContext = mPresContext->GetRootPresContext();
-  if (!rootPresContext) {
-    // In some edge cases, such as when we don't have a root frame yet,
-    // we can't find the root prescontext. There's nothing to do in that
-    // case.
-    return;
-  }
-
-  rootPresContext->FlushWillPaintObservers();
-  if (mIsDestroying) return;
-
   // Process reflows, if we have them, to reduce flicker due to invalidates and
   // reflow being interspersed.  Note that we _do_ allow this to be
   // interruptible; if we can't do all the reflows it's better to flicker a bit
diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
index 2a7cacb8350b..ea91dbe83332 100644
--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -2709,27 +2709,6 @@ void nsRootPresContext::CollectPluginGeometryUpdates(
 #endif  // #ifndef XP_MACOSX
 }
 
-void nsRootPresContext::AddWillPaintObserver(nsIRunnable* aRunnable) {
-  if (!mWillPaintFallbackEvent.IsPending()) {
-    mWillPaintFallbackEvent = new RunWillPaintObservers(this);
-    Document()->Dispatch(TaskCategory::Other,
-                         do_AddRef(mWillPaintFallbackEvent));
-  }
-  mWillPaintObservers.AppendElement(aRunnable);
-}
-
-/**
- * Run all runnables that need to get called before the next paint.
- */
-void nsRootPresContext::FlushWillPaintObservers() {
-  mWillPaintFallbackEvent = nullptr;
-  nsTArray<nsCOMPtr<nsIRunnable>> observers;
-  observers.SwapElements(mWillPaintObservers);
-  for (uint32_t i = 0; i < observers.Length(); ++i) {
-    observers[i]->Run();
-  }
-}
-
 size_t nsRootPresContext::SizeOfExcludingThis(
     MallocSizeOf aMallocSizeOf) const {
   return nsPresContext::SizeOfExcludingThis(aMallocSizeOf);
@@ -2737,6 +2716,4 @@ size_t nsRootPresContext::SizeOfExcludingThis(
   // Measurement of the following members may be added later if DMD finds it is
   // worthwhile:
   // - mRegisteredPlugins
-  // - mWillPaintObservers
-  // - mWillPaintFallbackEvent
 }
diff --git a/layout/base/nsPresContext.h b/layout/base/nsPresContext.h
index a100aa8e5e9d..8aea00347ae6 100644
--- a/layout/base/nsPresContext.h
+++ b/layout/base/nsPresContext.h
@@ -1354,18 +1354,6 @@ class nsRootPresContext final : public nsPresContext {
 
   virtual bool IsRoot() override { return true; }
 
-  /**
-   * Add a runnable that will get called before the next paint. They will get
-   * run eventually even if painting doesn't happen. They might run well before
-   * painting happens.
-   */
-  void AddWillPaintObserver(nsIRunnable* aRunnable);
-
-  /**
-   * Run all runnables that need to get called before the next paint.
-   */
-  void FlushWillPaintObservers();
-
   virtual size_t SizeOfExcludingThis(
       mozilla::MallocSizeOf aMallocSizeOf) const override;
 
@@ -1379,28 +1367,10 @@ class nsRootPresContext final : public nsPresContext {
    */
   void CancelApplyPluginGeometryTimer();
 
-  class RunWillPaintObservers : public mozilla::Runnable {
-   public:
-    explicit RunWillPaintObservers(nsRootPresContext* aPresContext)
-        : Runnable("nsPresContextType::RunWillPaintObservers"),
-          mPresContext(aPresContext) {}
-    void Revoke() { mPresContext = nullptr; }
-    NS_IMETHOD Run() override {
-      if (mPresContext) {
-        mPresContext->FlushWillPaintObservers();
-      }
-      return NS_OK;
-    }
-    // The lifetime of this reference is handled by an nsRevocableEventPtr
-    nsRootPresContext* MOZ_NON_OWNING_REF mPresContext;
-  };
-
   friend class nsPresContext;
 
   nsCOMPtr<nsITimer> mApplyPluginGeometryTimer;
   nsTHashtable<nsRefPtrHashKey<nsIContent>> mRegisteredPlugins;
-  nsTArray<nsCOMPtr<nsIRunnable>> mWillPaintObservers;
-  nsRevocableEventPtr<RunWillPaintObservers> mWillPaintFallbackEvent;
 };
 
 #ifdef MOZ_REFLOW_PERF
diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
index 4b1dfb86d455..1234faa51675 100644
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -5311,13 +5311,8 @@ void ScrollFrameHelper::PostOverflowEvent() {
     return;
   }
 
-  nsRootPresContext* rpc = mOuter->PresContext()->GetRootPresContext();
-  if (!rpc) {
-    return;
-  }
-
   mAsyncScrollPortEvent = new AsyncScrollPortEvent(this);
-  rpc->AddWillPaintObserver(mAsyncScrollPortEvent.get());
+  nsContentUtils::AddScriptRunner(mAsyncScrollPortEvent.get());
 }
 
 nsIFrame* ScrollFrameHelper::GetFrameForDir() const {