diff --git a/layout/style/ServoCSSRuleList.cpp b/layout/style/ServoCSSRuleList.cpp
index 808770095188..74136b549ec9 100644
--- a/layout/style/ServoCSSRuleList.cpp
+++ b/layout/style/ServoCSSRuleList.cpp
@@ -36,7 +36,9 @@ ServoCSSRuleList::ServoCSSRuleList(already_AddRefed<ServoCssRules> aRawRules,
                                    StyleSheet* aSheet,
                                    css::GroupRule* aParentRule)
     : mStyleSheet(aSheet), mParentRule(aParentRule), mRawRules(aRawRules) {
-  ResetRules();
+  if (mRawRules) {
+    Servo_CssRules_ListTypes(mRawRules, &mRules);
+  }
 }
 
 // QueryInterface implementation for ServoCSSRuleList
@@ -132,7 +134,10 @@ static void DropRule(already_AddRefed<css::Rule> aRule) {
   rule->DropReferences();
 }
 
-void ServoCSSRuleList::ResetRules() {
+void ServoCSSRuleList::DropAllRules() {
+  mStyleSheet = nullptr;
+  mParentRule = nullptr;
+  mRawRules = nullptr;
   // DropRule could reenter here via the cycle collector.
   auto rules = std::move(mRules);
   for (uintptr_t rule : rules) {
@@ -141,17 +146,6 @@ void ServoCSSRuleList::ResetRules() {
     }
   }
   MOZ_ASSERT(mRules.IsEmpty());
-  if (mRawRules) {
-    Servo_CssRules_ListTypes(mRawRules, &mRules);
-  }
-}
-
-void ServoCSSRuleList::DropAllRules() {
-  mStyleSheet = nullptr;
-  mParentRule = nullptr;
-  mRawRules = nullptr;
-
-  ResetRules();
 }
 
 void ServoCSSRuleList::DropSheetReference() {
@@ -227,14 +221,8 @@ nsresult ServoCSSRuleList::DeleteRule(uint32_t aIndex) {
   return rv;
 }
 
-void ServoCSSRuleList::SetRawContents(RefPtr<ServoCssRules> aNewRules,
-                                      bool aFromClone) {
+void ServoCSSRuleList::SetRawAfterClone(RefPtr<ServoCssRules> aNewRules) {
   mRawRules = std::move(aNewRules);
-  if (!aFromClone) {
-    ResetRules();
-    return;
-  }
-
   EnumerateInstantiatedRules([&](css::Rule* aRule, uint32_t aIndex) {
 #define CASE_FOR(constant_, type_)                                           \
   case StyleCssRuleType::constant_: {                                        \
diff --git a/layout/style/ServoCSSRuleList.h b/layout/style/ServoCSSRuleList.h
index 4c65e0097c21..18eefb3f04ff 100644
--- a/layout/style/ServoCSSRuleList.h
+++ b/layout/style/ServoCSSRuleList.h
@@ -48,13 +48,7 @@ class ServoCSSRuleList final : public dom::CSSRuleList {
   nsresult InsertRule(const nsACString& aRule, uint32_t aIndex);
   nsresult DeleteRule(uint32_t aIndex);
 
-  // aFromClone says whether this comes from a clone of the stylesheet (and thus
-  // we should also fix up the wrappers for the individual rules in the rule
-  // lists).
-  void SetRawContents(RefPtr<ServoCssRules>, bool aFromClone);
-  void SetRawAfterClone(RefPtr<ServoCssRules> aRules) {
-    SetRawContents(std::move(aRules), /* aFromClone = */ true);
-  }
+  void SetRawAfterClone(RefPtr<ServoCssRules>);
 
  private:
   virtual ~ServoCSSRuleList();
@@ -75,7 +69,6 @@ class ServoCSSRuleList final : public dom::CSSRuleList {
   void EnumerateInstantiatedRules(Func aCallback);
 
   void DropAllRules();
-  void ResetRules();
 
   bool IsReadOnly() const;
 
diff --git a/layout/style/StyleSheet.cpp b/layout/style/StyleSheet.cpp
index 3b2c02a61a3f..66d04666aa5b 100644
--- a/layout/style/StyleSheet.cpp
+++ b/layout/style/StyleSheet.cpp
@@ -773,8 +773,8 @@ void StyleSheet::ReplaceSync(const nsACString& aText, ErrorResult& aRv) {
           .Consume();
 
   // 5. Set sheet's rules to the new rules.
+  DropRuleList();
   Inner().mContents = std::move(rawContent);
-  FixUpRuleListAfterContentsChangeIfNeeded();
   FinishParse();
   RuleChanged(nullptr, StyleRuleChangeKind::Generic);
 }
@@ -1109,25 +1109,18 @@ JSObject* StyleSheet::WrapObject(JSContext* aCx,
   return dom::CSSStyleSheet_Binding::Wrap(aCx, this, aGivenProto);
 }
 
-void StyleSheet::FixUpRuleListAfterContentsChangeIfNeeded(bool aFromClone) {
-  if (!mRuleList) {
-    return;
-  }
-
-  RefPtr<ServoCssRules> rules =
-      Servo_StyleSheet_GetRules(Inner().mContents.get()).Consume();
-  mRuleList->SetRawContents(std::move(rules), aFromClone);
-}
-
 void StyleSheet::FixUpAfterInnerClone() {
   MOZ_ASSERT(Inner().mSheets.Length() == 1, "Should've just cloned");
   MOZ_ASSERT(Inner().mSheets[0] == this);
   MOZ_ASSERT(Inner().mChildren.IsEmpty());
 
-  FixUpRuleListAfterContentsChangeIfNeeded(/* aFromClone = */ true);
+  auto* contents = Inner().mContents.get();
+  RefPtr<ServoCssRules> rules = Servo_StyleSheet_GetRules(contents).Consume();
+
+  if (mRuleList) {
+    mRuleList->SetRawAfterClone(rules);
+  }
 
-  RefPtr<ServoCssRules> rules =
-      Servo_StyleSheet_GetRules(Inner().mContents.get()).Consume();
   uint32_t index = 0;
   while (true) {
     uint32_t line, column;  // Actually unused.
@@ -1336,11 +1329,11 @@ void StyleSheet::ReparseSheet(const nsACString& aInput, ErrorResult& aRv) {
     }
   }
 
+  DropRuleList();
+
   ParseSheetSync(loader, aInput, /* aLoadData = */ nullptr, lineNumber,
                  &reusableSheets);
 
-  FixUpRuleListAfterContentsChangeIfNeeded();
-
   // Notify the stylesets about the new rules.
   {
     // Get the rule list (which will need to be regenerated after ParseSheet).
diff --git a/layout/style/StyleSheet.h b/layout/style/StyleSheet.h
index d68f1a0cac33..128bd4dbce74 100644
--- a/layout/style/StyleSheet.h
+++ b/layout/style/StyleSheet.h
@@ -516,11 +516,6 @@ class StyleSheet final : public nsICSSLoaderObserver, public nsWrapperCache {
   // correctly to `aPrimarySheet`.
   void FixUpAfterInnerClone();
 
-  // aFromClone says whether this comes from a clone of the stylesheet (and thus
-  // we should also fix up the wrappers for the individual rules in the rule
-  // lists).
-  void FixUpRuleListAfterContentsChangeIfNeeded(bool aFromClone = false);
-
   void DropRuleList();
 
   // Called when a rule is removed from the sheet from CSSOM.
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index 1f7908c26a64..0af459383c52 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -7330,7 +7330,7 @@
 # Whether Constructable Stylesheets are enabled in script.
 - name: layout.css.constructable-stylesheets.enabled
   type: bool
-  value: true
+  value: false
   mirror: always
 
 # Whether trigonometric constants and functions are enabled in calc().
diff --git a/testing/web-platform/tests/css/cssom/CSSStyleSheet-constructable-cssRules.html b/testing/web-platform/tests/css/cssom/CSSStyleSheet-constructable-cssRules.html
deleted file mode 100644
index 72b0e15c8b84..000000000000
--- a/testing/web-platform/tests/css/cssom/CSSStyleSheet-constructable-cssRules.html
+++ /dev/null
@@ -1,22 +0,0 @@
-<!doctype html>
-<meta charset="utf-8">
-<title>CSSStyleSheet.replace/replaceSync() doesn't change cssRules object</title>
-<link rel="author" href="mailto:emilio@crisal.io" title="Emilio Cobos Álvarez">
-<link rel="author" href="https://mozilla.org" title="Mozilla">
-<link rel="help" href="https://drafts.csswg.org/cssom/#extensions-to-the-document-or-shadow-root-interface">
-<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1752392">
-<script src="/resources/testharness.js"></script>
-<script src="/resources/testharnessreport.js"></script>
-<span>Should be green</span>
-<script>
-promise_test(async function() {
-  const sheet = new CSSStyleSheet();
-  let rules = sheet.cssRules;
-  sheet.replaceSync('span {color:blue;}');
-  assert_equals(rules, sheet.cssRules, "Rules should be the same after replaceSync");
-  await sheet.replace('span {color: lime;}');
-  assert_equals(rules, sheet.cssRules, "Rules should be the same after replace()");
-  document.adoptedStyleSheets = [sheet];
-  assert_equals(getComputedStyle(document.querySelector("span")).color, "rgb(0, 255, 0)", "Sheet should apply");
-}, "cssRules doesn't change on replace / replaceSync");
-</script>
diff --git a/toolkit/components/featuregates/Features.toml b/toolkit/components/featuregates/Features.toml
index ed509f43dc01..ac719e3db76c 100644
--- a/toolkit/components/featuregates/Features.toml
+++ b/toolkit/components/featuregates/Features.toml
@@ -40,7 +40,7 @@ preference = "layout.css.constructable-stylesheets.enabled"
 type = "boolean"
 bug-numbers = [1520690]
 is-public = {default = false, nightly = true}
-default-value = true
+default-value = false
 
 [devtools-compatibility-panel]
 title = "experimental-features-devtools-compatibility-panel"