diff --git a/dom/base/nsDOMWindowUtils.cpp b/dom/base/nsDOMWindowUtils.cpp
index 6d611b4a8485..b2cc65940a8c 100644
--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -4287,61 +4287,6 @@ struct StateTableEntry {
   ElementState mState;
 };
 
-static constexpr StateTableEntry kManuallyManagedStates[] = {
-    {"autofill", ElementState::AUTOFILL},
-    // :-moz-autofill-preview implies :autofill.
-    {"-moz-autofill-preview",
-     ElementState::AUTOFILL_PREVIEW | ElementState::AUTOFILL},
-    {nullptr, ElementState()},
-};
-
-static_assert(!kManuallyManagedStates[ArrayLength(kManuallyManagedStates) - 1]
-                   .mStateString,
-              "last kManuallyManagedStates entry must be a sentinel with "
-              "mStateString == nullptr");
-
-static ElementState GetEventStateForString(const nsAString& aStateString) {
-  for (const StateTableEntry* entry = kManuallyManagedStates;
-       entry->mStateString; ++entry) {
-    if (aStateString.EqualsASCII(entry->mStateString)) {
-      return entry->mState;
-    }
-  }
-  return ElementState();
-}
-
-NS_IMETHODIMP
-nsDOMWindowUtils::AddManuallyManagedState(Element* aElement,
-                                          const nsAString& aStateString) {
-  if (!aElement) {
-    return NS_ERROR_INVALID_ARG;
-  }
-
-  ElementState state = GetEventStateForString(aStateString);
-  if (state.IsEmpty()) {
-    return NS_ERROR_INVALID_ARG;
-  }
-
-  aElement->AddStates(state);
-  return NS_OK;
-}
-
-NS_IMETHODIMP
-nsDOMWindowUtils::RemoveManuallyManagedState(Element* aElement,
-                                             const nsAString& aStateString) {
-  if (!aElement) {
-    return NS_ERROR_INVALID_ARG;
-  }
-
-  ElementState state = GetEventStateForString(aStateString);
-  if (state.IsEmpty()) {
-    return NS_ERROR_INVALID_ARG;
-  }
-
-  aElement->RemoveStates(state);
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 nsDOMWindowUtils::GetStorageUsage(Storage* aStorage, int64_t* aRetval) {
   if (!aStorage) {
diff --git a/dom/interfaces/base/nsIDOMWindowUtils.idl b/dom/interfaces/base/nsIDOMWindowUtils.idl
index 9d185e8e7edc..253ceb727259 100644
--- a/dom/interfaces/base/nsIDOMWindowUtils.idl
+++ b/dom/interfaces/base/nsIDOMWindowUtils.idl
@@ -2070,26 +2070,6 @@ interface nsIDOMWindowUtils : nsISupports {
     */
   readonly attribute int32_t gpuProcessPid;
 
-  /**
-   * Adds an ElementState bit to the element.
-   *
-   * The state string must be one of the following:
-   *   * (none yet; but for example "higlighted" for ElementState::HIGHLIGHTED)
-   *
-   * The supported state strings are defined in kManuallyManagedStates
-   * in nsDOMWindowUtils.cpp.
-   */
-  void addManuallyManagedState(in Element element,
-                               in AString state);
-
-  /**
-   * Removes the specified ElementState bits from the element.
-   *
-   * See above for the strings that can be passed for |state|.
-   */
-  void removeManuallyManagedState(in Element element,
-                                  in AString state);
-
   /**
    * Returns usage data for a given storage object.
    *
diff --git a/layout/reftests/forms/input/text/autofill-author-background.html b/layout/reftests/forms/input/text/autofill-author-background.html
index 73eb71ea7c3f..0e8fe408d227 100644
--- a/layout/reftests/forms/input/text/autofill-author-background.html
+++ b/layout/reftests/forms/input/text/autofill-author-background.html
@@ -5,5 +5,5 @@
   SpecialPowers.Cc["@mozilla.org/satchel/form-fill-controller;1"].getService(SpecialPowers.Ci.nsIFormFillController).markAsAutoCompletableField(input);
   input.getBoundingClientRect(); // previewValue setter depends on the reframe posted by markAsAutoCompletableField() having being processed...
   input.previewValue = "Autofill";
-  SpecialPowers.wrap(window).windowUtils.addManuallyManagedState(input, "-moz-autofill-preview");
+  input.autofillState = "preview";
 </script>
diff --git a/layout/reftests/forms/input/text/autofill-blank.html b/layout/reftests/forms/input/text/autofill-blank.html
index 17919875eea4..6373dea1b2f3 100644
--- a/layout/reftests/forms/input/text/autofill-blank.html
+++ b/layout/reftests/forms/input/text/autofill-blank.html
@@ -4,5 +4,5 @@
   let input = SpecialPowers.wrap(document.querySelector("input"));
   SpecialPowers.Cc["@mozilla.org/satchel/form-fill-controller;1"].getService(SpecialPowers.Ci.nsIFormFillController).markAsAutoCompletableField(input);
   input.getBoundingClientRect();
-  SpecialPowers.wrap(window).windowUtils.addManuallyManagedState(input, "autofill");
+  input.autofillState = "autofill";
 </script>
diff --git a/layout/reftests/forms/input/text/autofill-line-height.html b/layout/reftests/forms/input/text/autofill-line-height.html
index 7ef597089682..8176f8334cee 100644
--- a/layout/reftests/forms/input/text/autofill-line-height.html
+++ b/layout/reftests/forms/input/text/autofill-line-height.html
@@ -5,5 +5,5 @@
 <input value="Autofill">
 <script>
   let input = SpecialPowers.wrap(document.querySelector("input"));
-  SpecialPowers.wrap(window).windowUtils.addManuallyManagedState(input, "autofill");
+  input.autofillState = "autofill";
 </script>
diff --git a/layout/reftests/forms/input/text/autofill-prefilled-value.html b/layout/reftests/forms/input/text/autofill-prefilled-value.html
index 07b4ce5310a3..0676fee4965f 100644
--- a/layout/reftests/forms/input/text/autofill-prefilled-value.html
+++ b/layout/reftests/forms/input/text/autofill-prefilled-value.html
@@ -5,5 +5,5 @@
   SpecialPowers.Cc["@mozilla.org/satchel/form-fill-controller;1"].getService(SpecialPowers.Ci.nsIFormFillController).markAsAutoCompletableField(input);
   input.getBoundingClientRect(); // previewValue setter depends on the reframe posted by markAsAutoCompletableField() having being processed...
   input.previewValue = "Autofill";
-  SpecialPowers.wrap(window).windowUtils.addManuallyManagedState(input, "-moz-autofill-preview");
+  input.autofillState = "preview";
 </script>
diff --git a/layout/reftests/forms/input/text/autofill-preview-blank.html b/layout/reftests/forms/input/text/autofill-preview-blank.html
index e441b80700f2..be6414166db9 100644
--- a/layout/reftests/forms/input/text/autofill-preview-blank.html
+++ b/layout/reftests/forms/input/text/autofill-preview-blank.html
@@ -4,5 +4,5 @@
   let input = SpecialPowers.wrap(document.querySelector("input"));
   SpecialPowers.Cc["@mozilla.org/satchel/form-fill-controller;1"].getService(SpecialPowers.Ci.nsIFormFillController).markAsAutoCompletableField(input);
   input.getBoundingClientRect();
-  SpecialPowers.wrap(window).windowUtils.addManuallyManagedState(input, "-moz-autofill-preview");
+  input.autofillState = "preview";
 </script>
diff --git a/layout/reftests/forms/input/text/autofill-preview-line-height.html b/layout/reftests/forms/input/text/autofill-preview-line-height.html
index 40b63e9ede66..71961121a03b 100644
--- a/layout/reftests/forms/input/text/autofill-preview-line-height.html
+++ b/layout/reftests/forms/input/text/autofill-preview-line-height.html
@@ -8,5 +8,5 @@
   SpecialPowers.Cc["@mozilla.org/satchel/form-fill-controller;1"].getService(SpecialPowers.Ci.nsIFormFillController).markAsAutoCompletableField(input);
   input.getBoundingClientRect(); // previewValue setter depends on the reframe posted by markAsAutoCompletableField() having being processed...
   input.previewValue = "Autofill";
-  SpecialPowers.wrap(window).windowUtils.addManuallyManagedState(input, "-moz-autofill-preview");
+  input.autofillState = "preview";
 </script>
diff --git a/layout/reftests/forms/input/text/autofill-preview.html b/layout/reftests/forms/input/text/autofill-preview.html
index 540c07423f03..c73153731a24 100644
--- a/layout/reftests/forms/input/text/autofill-preview.html
+++ b/layout/reftests/forms/input/text/autofill-preview.html
@@ -5,5 +5,5 @@
   SpecialPowers.Cc["@mozilla.org/satchel/form-fill-controller;1"].getService(SpecialPowers.Ci.nsIFormFillController).markAsAutoCompletableField(input);
   input.getBoundingClientRect(); // previewValue setter depends on the reframe posted by markAsAutoCompletableField() having being processed...
   input.previewValue = "Autofill";
-  SpecialPowers.wrap(window).windowUtils.addManuallyManagedState(input, "-moz-autofill-preview");
+  input.autofillState = "preview";
 </script>
diff --git a/layout/reftests/forms/input/text/autofill.html b/layout/reftests/forms/input/text/autofill.html
index 0d9c6a058824..934ccfb4956e 100644
--- a/layout/reftests/forms/input/text/autofill.html
+++ b/layout/reftests/forms/input/text/autofill.html
@@ -5,5 +5,5 @@
   SpecialPowers.Cc["@mozilla.org/satchel/form-fill-controller;1"].getService(SpecialPowers.Ci.nsIFormFillController).markAsAutoCompletableField(input);
   input.getBoundingClientRect(); // previewValue setter depends on the reframe posted by markAsAutoCompletableField() having being processed...
   input.previewValue = "Autofill";
-  SpecialPowers.wrap(window).windowUtils.addManuallyManagedState(input, "autofill");
+  input.autofillState = "autofill";
 </script>
diff --git a/toolkit/modules/tests/modules/MockDocument.sys.mjs b/toolkit/modules/tests/modules/MockDocument.sys.mjs
index d4c2b0720539..a4061259551a 100644
--- a/toolkit/modules/tests/modules/MockDocument.sys.mjs
+++ b/toolkit/modules/tests/modules/MockDocument.sys.mjs
@@ -59,10 +59,6 @@ export const MockDocument = {
   mockOwnerGlobalProperty(aElement) {
     Object.defineProperty(aElement, "ownerGlobal", {
       value: {
-        windowUtils: {
-          addManuallyManagedState() {},
-          removeManuallyManagedState() {},
-        },
         UIEvent: Event,
         Event,
       },