diff --git a/dom/events/EventStates.h b/dom/events/EventStates.h
index 291530d86b..38a3618ba7 100644
--- a/dom/events/EventStates.h
+++ b/dom/events/EventStates.h
@@ -293,6 +293,9 @@ private:
 // Modal <dialog> element
 #define NS_EVENT_STATE_MODAL_DIALOG NS_DEFINE_EVENT_STATE_MACRO(54)
 
+// Autofilled input element (for :autofill pseudo-class)
+#define NS_EVENT_STATE_AUTOFILL NS_DEFINE_EVENT_STATE_MACRO(55)
+
 #define DIR_ATTR_STATES (NS_EVENT_STATE_HAS_DIR_ATTR |          \
                          NS_EVENT_STATE_DIR_ATTR_LTR |          \
                          NS_EVENT_STATE_DIR_ATTR_RTL |          \
diff --git a/dom/html/HTMLInputElement.cpp b/dom/html/HTMLInputElement.cpp
index 374fb14ef1..6a0979fce0 100644
--- a/dom/html/HTMLInputElement.cpp
+++ b/dom/html/HTMLInputElement.cpp
@@ -2832,6 +2832,16 @@ HTMLInputElement::SetUserInput(const nsAString& aValue)
   return NS_OK;
 }
 
+void
+HTMLInputElement::SetAutofilled(bool aAutofilled)
+{
+  if (aAutofilled) {
+    AddStates(NS_EVENT_STATE_AUTOFILL);
+  } else {
+    RemoveStates(NS_EVENT_STATE_AUTOFILL);
+  }
+}
+
 nsIEditor*
 HTMLInputElement::GetEditor()
 {
@@ -8507,6 +8517,11 @@ HTMLInputElement::OnValueChanged(bool aNotify, bool aWasInteractiveUserChange)
 {
   mLastValueChangeWasInteractive = aWasInteractiveUserChange;
 
+  // Clear autofilled state if this was an interactive user change
+  if (aWasInteractiveUserChange && State().HasState(NS_EVENT_STATE_AUTOFILL)) {
+    RemoveStates(NS_EVENT_STATE_AUTOFILL);
+  }
+
   UpdateAllValidityStates(aNotify);
 
   if (HasDirAuto()) {
diff --git a/dom/html/HTMLInputElement.h b/dom/html/HTMLInputElement.h
index e46be30ea7..36c4b06c0b 100644
--- a/dom/html/HTMLInputElement.h
+++ b/dom/html/HTMLInputElement.h
@@ -845,6 +845,16 @@ public:
   void SetUserInput(const nsAString& aInput,
                     nsIPrincipal& aSubjectPrincipal);
 
+  /**
+   * Sets or clears the autofilled state of this input element.
+   * This is used by the browser's autofill system to indicate when
+   * a value has been automatically filled (e.g., from saved passwords
+   * or form data).
+   *
+   * @param aAutofilled Whether the element should be marked as autofilled
+   */
+  void SetAutofilled(bool aAutofilled);
+
   // XPCOM GetPhonetic() is OK
 
   /**
diff --git a/dom/html/HTMLTextAreaElement.cpp b/dom/html/HTMLTextAreaElement.cpp
index 48b28d3fe4..e34e56975f 100644
--- a/dom/html/HTMLTextAreaElement.cpp
+++ b/dom/html/HTMLTextAreaElement.cpp
@@ -366,6 +366,16 @@ HTMLTextAreaElement::SetUserInput(const nsAString& aValue)
   return SetValueInternal(aValue, nsTextEditorState::eSetValue_BySetUserInput);
 }
 
+void
+HTMLTextAreaElement::SetAutofilled(bool aAutofilled)
+{
+  if (aAutofilled) {
+    AddStates(NS_EVENT_STATE_AUTOFILL);
+  } else {
+    RemoveStates(NS_EVENT_STATE_AUTOFILL);
+  }
+}
+
 NS_IMETHODIMP
 HTMLTextAreaElement::SetValueChanged(bool aValueChanged)
 {
@@ -1633,6 +1643,11 @@ HTMLTextAreaElement::OnValueChanged(bool aNotify, bool aWasInteractiveUserChange
 {
   mLastValueChangeWasInteractive = aWasInteractiveUserChange;
 
+  // Clear autofilled state if this was an interactive user change
+  if (aWasInteractiveUserChange && State().HasState(NS_EVENT_STATE_AUTOFILL)) {
+    RemoveStates(NS_EVENT_STATE_AUTOFILL);
+  }
+
   // Update the validity state
   bool validBefore = IsValid();
   UpdateTooLongValidityState();
diff --git a/dom/html/HTMLTextAreaElement.h b/dom/html/HTMLTextAreaElement.h
index cc9c2b7c5c..4efc264e0b 100644
--- a/dom/html/HTMLTextAreaElement.h
+++ b/dom/html/HTMLTextAreaElement.h
@@ -70,6 +70,15 @@ public:
   }
   NS_IMETHOD SetUserInput(const nsAString& aInput) override;
 
+  /**
+   * Sets or clears the autofilled state of this textarea element.
+   * This is used by the browser's autofill system to indicate when
+   * a value has been automatically filled (e.g., from saved form data).
+   *
+   * @param aAutofilled Whether the element should be marked as autofilled
+   */
+  void SetAutofilled(bool aAutofilled);
+
   // nsIFormControl
   NS_IMETHOD_(uint32_t) GetType() const override { return NS_FORM_TEXTAREA; }
   NS_IMETHOD Reset() override;
diff --git a/dom/webidl/HTMLInputElement.webidl b/dom/webidl/HTMLInputElement.webidl
index 1eefaea61e..5d0d7895b9 100644
--- a/dom/webidl/HTMLInputElement.webidl
+++ b/dom/webidl/HTMLInputElement.webidl
@@ -200,6 +200,13 @@ partial interface HTMLInputElement {
   // for example will be dispatched when focusing out the element.
   [Func="IsChromeOrXBL", NeedsSubjectPrincipal]
   void setUserInput(DOMString input);
+
+  // Sets or clears the autofilled state of this input element.
+  // This is used by the browser's autofill system to indicate when
+  // a value has been automatically filled (e.g., from saved passwords
+  // or form data).
+  [ChromeOnly]
+  void setAutofilled(boolean autofilled);
 };
 
 partial interface HTMLInputElement {
diff --git a/dom/webidl/HTMLTextAreaElement.webidl b/dom/webidl/HTMLTextAreaElement.webidl
index 7a181bf394..5eb31b1dfa 100644
--- a/dom/webidl/HTMLTextAreaElement.webidl
+++ b/dom/webidl/HTMLTextAreaElement.webidl
@@ -97,4 +97,10 @@ partial interface HTMLTextAreaElement {
   // element.
   [ChromeOnly]
   void setUserInput(DOMString input);
+
+  // Sets or clears the autofilled state of this textarea element.
+  // This is used by the browser's autofill system to indicate when
+  // a value has been automatically filled (e.g., from saved form data).
+  [ChromeOnly]
+  void setAutofilled(boolean autofilled);
 };
diff --git a/layout/style/nsCSSPseudoClassList.h b/layout/style/nsCSSPseudoClassList.h
index 485a1a428d..b763be1283 100644
--- a/layout/style/nsCSSPseudoClassList.h
+++ b/layout/style/nsCSSPseudoClassList.h
@@ -194,6 +194,9 @@ CSS_STATE_PSEUDO_CLASS(mozFullScreen, ":-moz-full-screen", 0, "", NS_EVENT_STATE
 CSS_STATE_PSEUDO_CLASS(modal, ":modal", 0, "", NS_EVENT_STATE_MODAL_DIALOG)
 CSS_STATE_PSEUDO_CLASS(mozModalDialog, ":-moz-modal-dialog", 0, "", NS_EVENT_STATE_MODAL_DIALOG)
 
+// Matches autofilled input elements
+CSS_STATE_PSEUDO_CLASS(autofill, ":autofill", 0, "", NS_EVENT_STATE_AUTOFILL)
+
 // Matches if the element is focused and should show a focus ring
 CSS_STATE_PSEUDO_CLASS(mozFocusRing, ":-moz-focusring", 0, "", NS_EVENT_STATE_FOCUSRING)
 
diff --git a/toolkit/components/formautofill/FormAutofillContentService.js b/toolkit/components/formautofill/FormAutofillContentService.js
index ee8e978ad9..273697f221 100644
--- a/toolkit/components/formautofill/FormAutofillContentService.js
+++ b/toolkit/components/formautofill/FormAutofillContentService.js
@@ -238,6 +238,11 @@ FormHandler.prototype = {
       }
 
       fieldDetail.element.value = field.value;
+      
+      // Set the autofilled state on the element
+      if (typeof fieldDetail.element.setAutofilled === 'function') {
+        fieldDetail.element.setAutofilled(true);
+      }
     }
   },