diff --git a/chips/internal/chip-set.ts b/chips/internal/chip-set.ts
index 8fa151f43..2a0819926 100644
--- a/chips/internal/chip-set.ts
+++ b/chips/internal/chip-set.ts
@@ -7,21 +7,12 @@
 import {html, isServer, LitElement} from 'lit';
 import {queryAssignedElements} from 'lit/decorators.js';
 
-import {
-  polyfillARIAMixin,
-  polyfillElementInternalsAria,
-} from '../../internal/aria/aria.js';
-
 import {Chip} from './chip.js';
 
 /**
  * A chip set component.
  */
 export class ChipSet extends LitElement {
-  static {
-    polyfillARIAMixin(ChipSet);
-  }
-
   get chips() {
     return this.childElements.filter(
       (child): child is Chip => child instanceof Chip,
@@ -29,11 +20,9 @@ export class ChipSet extends LitElement {
   }
 
   @queryAssignedElements() private readonly childElements!: HTMLElement[];
-  private readonly internals = polyfillElementInternalsAria(
-    this,
+  private readonly internals =
     // Cast needed for closure
-    (this as HTMLElement).attachInternals(),
-  );
+    (this as HTMLElement).attachInternals();
 
   constructor() {
     super();
diff --git a/docs/support.md b/docs/support.md
index 971390c22..3349aec76 100644
--- a/docs/support.md
+++ b/docs/support.md
@@ -28,7 +28,7 @@ Browser | Version
 ------- | -------
 Chrome  | 112 +
 Edge    | 112 +
-Firefox | 113 +
+Firefox | 119 +
 Safari* | 16.4 +
 
 *\* previous versions of Safari may be supported with an
diff --git a/internal/aria/aria.ts b/internal/aria/aria.ts
index e223d5585..22f2c7f4d 100644
--- a/internal/aria/aria.ts
+++ b/internal/aria/aria.ts
@@ -4,8 +4,6 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import {isServer, ReactiveElement} from 'lit';
-
 /**
  * Accessibility Object Model reflective aria property name types.
  */
@@ -293,172 +291,3 @@ export type ARIARole =
   | 'doc-subtitle'
   | 'doc-tip'
   | 'doc-toc';
-
-/**
- * This function will polyfill `ARIAMixin` properties for Firefox.
- *
- * @param ctor The `ReactiveElement` constructor to set up.
- */
-export function polyfillARIAMixin(ctor: typeof ReactiveElement) {
-  if (isServer || 'role' in Element.prototype) {
-    return;
-  }
-
-  // Polyfill reflective aria properties for Firefox
-  for (const ariaProperty of ARIA_PROPERTIES) {
-    ctor.createProperty(ariaProperty, {
-      attribute: ariaPropertyToAttribute(ariaProperty),
-      reflect: true,
-    });
-  }
-
-  ctor.createProperty('role', {reflect: true});
-}
-
-/**
- * Polyfills an element and its `ElementInternals` to support `ARIAMixin`
- * properties on internals. This is needed for Firefox.
- *
- * `polyfillARIAMixin()` must be called for the element class.
- *
- * @example
- * class XButton extends LitElement {
- *   static {
- *     polyfillARIAMixin(XButton);
- *   }
- *
- *   private internals =
- *       polyfillElementInternalsAria(this, this.attachInternals());
- *
- *   constructor() {
- *     super();
- *     this.internals.role = 'button';
- *   }
- * }
- */
-export function polyfillElementInternalsAria(
-  host: ReactiveElement,
-  internals: ElementInternals,
-) {
-  if (checkIfElementInternalsSupportsAria(internals)) {
-    return internals;
-  }
-
-  if (!('role' in host)) {
-    throw new Error('Missing polyfillARIAMixin()');
-  }
-
-  let firstConnectedCallbacks: Array<{
-    property: ARIAProperty | 'role';
-    callback: () => void;
-  }> = [];
-  let hasBeenConnected = false;
-
-  // Add support for Firefox, which has not yet implement ElementInternals aria
-  for (const ariaProperty of ARIA_PROPERTIES) {
-    let internalAriaValue: string | null = null;
-    Object.defineProperty(internals, ariaProperty, {
-      enumerable: true,
-      configurable: true,
-      get() {
-        return internalAriaValue;
-      },
-      set(value: string | null) {
-        const setValue = () => {
-          internalAriaValue = value;
-          if (!hasBeenConnected) {
-            firstConnectedCallbacks.push({
-              property: ariaProperty,
-              callback: setValue,
-            });
-            return;
-          }
-
-          // Dynamic lookup rather than hardcoding all properties.
-          // tslint:disable-next-line:no-dict-access-on-struct-type
-          host[ariaProperty] = value;
-        };
-
-        setValue();
-      },
-    });
-  }
-
-  let internalRoleValue: string | null = null;
-  Object.defineProperty(internals, 'role', {
-    enumerable: true,
-    configurable: true,
-    get() {
-      return internalRoleValue;
-    },
-    set(value: string | null) {
-      const setRole = () => {
-        internalRoleValue = value;
-
-        if (!hasBeenConnected) {
-          firstConnectedCallbacks.push({
-            property: 'role',
-            callback: setRole,
-          });
-          return;
-        }
-
-        if (value === null) {
-          host.removeAttribute('role');
-        } else {
-          host.setAttribute('role', value);
-        }
-      };
-
-      setRole();
-    },
-  });
-
-  host.addController({
-    hostConnected() {
-      if (hasBeenConnected) {
-        return;
-      }
-
-      hasBeenConnected = true;
-
-      const propertiesSetByUser = new Set<ARIAProperty | 'role'>();
-
-      // See which properties were set by the user on host before we apply
-      // internals values as attributes to host. Needs to be done in another
-      // for loop because the callbacks set these attributes on host.
-      for (const {property} of firstConnectedCallbacks) {
-        const wasSetByUser =
-          host.getAttribute(ariaPropertyToAttribute(property)) !== null ||
-          // Dynamic lookup rather than hardcoding all properties.
-          // tslint:disable-next-line:no-dict-access-on-struct-type
-          host[property] !== undefined;
-
-        if (wasSetByUser) {
-          propertiesSetByUser.add(property);
-        }
-      }
-
-      for (const {property, callback} of firstConnectedCallbacks) {
-        // If the user has set the attribute or property, do not override the
-        // user's value
-        if (propertiesSetByUser.has(property)) {
-          continue;
-        }
-
-        callback();
-      }
-
-      // Remove strong callback references
-      firstConnectedCallbacks = [];
-    },
-  });
-
-  return internals;
-}
-
-// Separate function so that typescript doesn't complain about internals being
-// "never".
-function checkIfElementInternalsSupportsAria(internals: ElementInternals) {
-  return 'role' in internals;
-}
diff --git a/internal/aria/aria_test.ts b/internal/aria/aria_test.ts
index efa2dafde..7ae577f59 100644
--- a/internal/aria/aria_test.ts
+++ b/internal/aria/aria_test.ts
@@ -6,16 +6,7 @@
 
 // import 'jasmine'; (google3-only)
 
-import {html, LitElement} from 'lit';
-import {customElement} from 'lit/decorators.js';
-
-import {
-  ARIAProperty,
-  ariaPropertyToAttribute,
-  isAriaAttribute,
-  polyfillARIAMixin,
-  polyfillElementInternalsAria,
-} from './aria.js';
+import {ARIAProperty, ariaPropertyToAttribute, isAriaAttribute} from './aria.js';
 
 describe('aria', () => {
   describe('isAriaAttribute()', () => {
@@ -51,277 +42,4 @@ describe('aria', () => {
       ).toBe('aria-labelledby');
     });
   });
-
-  describe('polyfillARIAMixin()', () => {
-    @customElement('test-setup-aria-host')
-    class TestElement extends LitElement {
-      static {
-        polyfillARIAMixin(TestElement);
-      }
-
-      override render() {
-        return html`<slot></slot>`;
-      }
-    }
-
-    it('should reflect ARIAMixin properties to attributes', async () => {
-      const element = new TestElement();
-      document.body.appendChild(element);
-      element.role = 'button';
-      element.ariaLabel = 'Foo';
-      await element.updateComplete;
-      expect(element.getAttribute('role'))
-        .withContext('role attribute value')
-        .toEqual('button');
-
-      expect(element.getAttribute('aria-label'))
-        .withContext('aria-label attribute value')
-        .toEqual('Foo');
-      element.remove();
-    });
-  });
-
-  describe('polyfillElementInternalsAria()', () => {
-    @customElement('test-polyfill-element-internals-aria')
-    class TestElement extends LitElement {
-      static {
-        polyfillARIAMixin(TestElement);
-      }
-
-      internals = polyfillElementInternalsAria(this, this.attachInternals());
-
-      constructor() {
-        super();
-        this.internals.role = 'button';
-      }
-
-      override render() {
-        return html`<slot></slot>`;
-      }
-    }
-
-    if ('role' in ElementInternals.prototype) {
-      it('should not hydrate attributes when role set', () => {
-        const element = new TestElement();
-        document.body.appendChild(element);
-        expect(element.hasAttribute('role'))
-          .withContext('has role attribute')
-          .toBeFalse();
-
-        element.remove();
-      });
-    } else {
-      it('should preserve role values when set before connected', () => {
-        const element = new TestElement();
-        // TestElement() sets role in constructor
-        expect(element.internals.role)
-          .withContext('ElementInternals.role')
-          .toEqual('button');
-      });
-
-      it('should preserve aria values when set before connected', () => {
-        const element = new TestElement();
-        element.internals.ariaLabel = 'Foo';
-        expect(element.internals.ariaLabel)
-          .withContext('ElementInternals.ariaLabel')
-          .toEqual('Foo');
-      });
-
-      it('should hydrate role attributes when set before connection', async () => {
-        const element = new TestElement();
-        // TestElement() sets role in constructor
-        document.body.appendChild(element);
-        await element.updateComplete;
-        expect(element.getAttribute('role'))
-          .withContext('role attribute value')
-          .toEqual('button');
-
-        element.remove();
-      });
-
-      it('should hydrate aria attributes when set before connection', async () => {
-        const element = new TestElement();
-        element.internals.ariaLabel = 'Foo';
-        document.body.appendChild(element);
-        await element.updateComplete;
-        expect(element.getAttribute('aria-label'))
-          .withContext('aria-label attribute value')
-          .toEqual('Foo');
-
-        element.remove();
-      });
-
-      it('should set aria attributes when set after connection', async () => {
-        const element = new TestElement();
-        document.body.appendChild(element);
-        element.internals.ariaLabel = 'Value after construction';
-        await element.updateComplete;
-        expect(element.getAttribute('aria-label'))
-          .withContext('aria-label attribute value')
-          .toEqual('Value after construction');
-
-        element.remove();
-      });
-
-      it('should not override aria attributes on host when set before connection', async () => {
-        const element = new TestElement();
-        element.setAttribute('aria-label', 'Value set by user');
-        element.internals.ariaLabel = 'Value set on internals';
-        document.body.appendChild(element);
-        await element.updateComplete;
-        expect(element.getAttribute('aria-label'))
-          .withContext('aria-label attribute value on host')
-          .toEqual('Value set by user');
-        expect(element.internals.ariaLabel)
-          .withContext('ariaLabel internals property still the same')
-          .toEqual('Value set on internals');
-
-        element.remove();
-      });
-
-      it('should not override aria properties on host when set before connection', async () => {
-        const element = new TestElement();
-        element.ariaLabel = 'Value set by user';
-        element.internals.ariaLabel = 'Value set on internals';
-        document.body.appendChild(element);
-        await element.updateComplete;
-        expect(element.getAttribute('aria-label'))
-          .withContext('aria-label attribute value on host')
-          .toEqual('Value set by user');
-        expect(element.ariaLabel)
-          .withContext('ariaLabel property value on host')
-          .toEqual('Value set by user');
-        expect(element.internals.ariaLabel)
-          .withContext('ariaLabel internals property still the same')
-          .toEqual('Value set on internals');
-
-        element.remove();
-      });
-
-      it('should not override role attribute on host when set before connection', async () => {
-        const element = new TestElement();
-        element.setAttribute('role', 'Value set by user');
-        element.internals.role = 'Value set on internals';
-        document.body.appendChild(element);
-        await element.updateComplete;
-        expect(element.getAttribute('role'))
-          .withContext('role attribute value on host')
-          .toEqual('Value set by user');
-        expect(element.internals.role)
-          .withContext('role internals property still the same')
-          .toEqual('Value set on internals');
-
-        element.remove();
-      });
-
-      it('should not override role property on host when set before connection', async () => {
-        const element = new TestElement();
-        element.role = 'Value set by user';
-        element.internals.role = 'Value set on internals';
-        document.body.appendChild(element);
-        await element.updateComplete;
-        expect(element.getAttribute('role'))
-          .withContext('role attribute value on host')
-          .toEqual('Value set by user');
-        expect(element.role)
-          .withContext('role property value on host')
-          .toEqual('Value set by user');
-        expect(element.internals.role)
-          .withContext('role internals property still the same')
-          .toEqual('Value set on internals');
-
-        element.remove();
-      });
-
-      it('should handle setting role multiple times before connection', async () => {
-        const element = new TestElement();
-        element.internals.role = 'button';
-        element.internals.role = 'checkbox';
-
-        expect(element.internals.role)
-          .withContext('internals.role before connection')
-          .toEqual('checkbox');
-        document.body.appendChild(element);
-        await element.updateComplete;
-        expect(element.internals.role)
-          .withContext('internals.role after connection')
-          .toEqual('checkbox');
-
-        element.remove();
-      });
-
-      it('should handle setting role multiple times before connection when property is set on host', async () => {
-        const element = new TestElement();
-        element.role = 'radio';
-        element.internals.role = 'button';
-        element.internals.role = 'checkbox';
-
-        expect(element.internals.role)
-          .withContext('internals.role before connection')
-          .toEqual('checkbox');
-        document.body.appendChild(element);
-        await element.updateComplete;
-        expect(element.internals.role)
-          .withContext('internals.role after connection')
-          .toEqual('checkbox');
-
-        element.remove();
-      });
-
-      it('should handle setting aria properties multiple times before connection', async () => {
-        const element = new TestElement();
-        element.internals.ariaLabel = 'First';
-        element.internals.ariaLabel = 'Second';
-
-        expect(element.internals.ariaLabel)
-          .withContext('internals.ariaLabel before connection')
-          .toEqual('Second');
-        document.body.appendChild(element);
-        await element.updateComplete;
-        expect(element.internals.ariaLabel)
-          .withContext('internals.ariaLabel after connection')
-          .toEqual('Second');
-
-        element.remove();
-      });
-
-      it('should handle setting aria properties multiple times before connection when property is set on host', async () => {
-        const element = new TestElement();
-        element.ariaLabel = 'First';
-        element.internals.ariaLabel = 'First';
-        element.internals.ariaLabel = 'Second';
-
-        expect(element.internals.ariaLabel)
-          .withContext('internals.ariaLabel before connection')
-          .toEqual('Second');
-        document.body.appendChild(element);
-        await element.updateComplete;
-        expect(element.internals.ariaLabel)
-          .withContext('internals.ariaLabel after connection')
-          .toEqual('Second');
-
-        element.remove();
-      });
-
-      it('should handle setting role after first connection while disconnected', async () => {
-        const element = new TestElement();
-        element.internals.role = 'button';
-        document.body.appendChild(element);
-        await element.updateComplete;
-
-        element.remove();
-        element.internals.role = 'checkbox';
-        expect(element.internals.role)
-          .withContext('internals.role after connected and disconnected')
-          .toEqual('checkbox');
-        document.body.appendChild(element);
-        await element.updateComplete;
-        expect(element.internals.role)
-          .withContext('internals.role after reconnected')
-          .toEqual('checkbox');
-
-        element.remove();
-      });
-    }
-  });
 });
diff --git a/labs/behaviors/element-internals.ts b/labs/behaviors/element-internals.ts
index 49468e77b..34b88bec6 100644
--- a/labs/behaviors/element-internals.ts
+++ b/labs/behaviors/element-internals.ts
@@ -6,10 +6,6 @@
 
 import {LitElement} from 'lit';
 
-import {
-  polyfillARIAMixin,
-  polyfillElementInternalsAria,
-} from '../../internal/aria/aria.js';
 import {MixinBase, MixinReturn} from './mixin.js';
 
 /**
@@ -61,21 +57,12 @@ export function mixinElementInternals<T extends MixinBase<LitElement>>(
     extends base
     implements WithElementInternals
   {
-    static {
-      polyfillARIAMixin(
-        WithElementInternalsElement as unknown as typeof LitElement,
-      );
-    }
-
     get [internals]() {
       // Create internals in getter so that it can be used in methods called on
       // construction in `ReactiveElement`, such as `requestUpdate()`.
       if (!this[privateInternals]) {
         // Cast needed for closure
-        this[privateInternals] = polyfillElementInternalsAria(
-          this,
-          (this as HTMLElement).attachInternals(),
-        );
+        this[privateInternals] = (this as HTMLElement).attachInternals();
       }
 
       return this[privateInternals];
diff --git a/list/internal/list.ts b/list/internal/list.ts
index bf0ce07c3..c5ec9dbb9 100644
--- a/list/internal/list.ts
+++ b/list/internal/list.ts
@@ -7,11 +7,6 @@
 import {html, isServer, LitElement} from 'lit';
 import {queryAssignedElements} from 'lit/decorators.js';
 
-import {
-  polyfillARIAMixin,
-  polyfillElementInternalsAria,
-} from '../../internal/aria/aria.js';
-
 import {ListController, NavigableKeys} from './list-controller.js';
 import {ListItem as SharedListItem} from './list-navigation-helpers.js';
 
@@ -23,10 +18,6 @@ interface ListItem extends SharedListItem {
 
 // tslint:disable-next-line:enforce-comments-on-exported-symbols
 export class List extends LitElement {
-  static {
-    polyfillARIAMixin(List);
-  }
-
   /**
    * An array of activatable and disableable list items. Queries every assigned
    * element that has the `md-list-item` attribute.
@@ -58,11 +49,9 @@ export class List extends LitElement {
     isActivatable: (item) => !item.disabled && item.type !== 'text',
   });
 
-  private readonly internals = polyfillElementInternalsAria(
-    this,
+  private readonly internals =
     // Cast needed for closure
-    (this as HTMLElement).attachInternals(),
-  );
+    (this as HTMLElement).attachInternals();
 
   constructor() {
     super();
diff --git a/menu/internal/menu.ts b/menu/internal/menu.ts
index 090c03f12..2afca9356 100644
--- a/menu/internal/menu.ts
+++ b/menu/internal/menu.ts
@@ -12,10 +12,6 @@ import {property, query, queryAssignedElements, state} from 'lit/decorators.js';
 import {ClassInfo, classMap} from 'lit/directives/class-map.js';
 import {styleMap} from 'lit/directives/style-map.js';
 
-import {
-  polyfillARIAMixin,
-  polyfillElementInternalsAria,
-} from '../../internal/aria/aria.js';
 import {EASING, createAnimationSignal} from '../../internal/motion/animation.js';
 import {
   ListController,
@@ -90,10 +86,6 @@ function getFocusedElement(
  * @fires closed {Event} Fired once the menu is closed, after any animations
  */
 export abstract class Menu extends LitElement {
-  static {
-    polyfillARIAMixin(Menu);
-  }
-
   @query('.menu') private readonly surfaceEl!: HTMLElement | null;
   @query('slot') private readonly slotEl!: HTMLSlotElement | null;
 
@@ -341,11 +333,9 @@ export abstract class Menu extends LitElement {
     this.requestUpdate('anchorElement');
   }
 
-  private readonly internals = polyfillElementInternalsAria(
-    this,
+  private readonly internals =
     // Cast needed for closure
-    (this as HTMLElement).attachInternals(),
-  );
+    (this as HTMLElement).attachInternals();
 
   constructor() {
     super();
diff --git a/tabs/internal/tab.ts b/tabs/internal/tab.ts
index 5a1925902..ae064554c 100644
--- a/tabs/internal/tab.ts
+++ b/tabs/internal/tab.ts
@@ -18,10 +18,6 @@ import {
 } from 'lit/decorators.js';
 import {ClassInfo, classMap} from 'lit/directives/class-map.js';
 
-import {
-  polyfillARIAMixin,
-  polyfillElementInternalsAria,
-} from '../../internal/aria/aria.js';
 import {EASING} from '../../internal/motion/animation.js';
 import {mixinFocusable} from '../../labs/behaviors/focusable.js';
 
@@ -44,10 +40,6 @@ const tabBaseClass = mixinFocusable(LitElement);
  * Tab component.
  */
 export class Tab extends tabBaseClass {
-  static {
-    polyfillARIAMixin(Tab);
-  }
-
   /**
    * The attribute `md-tab` indicates that the element is a tab for the parent
    * element, `<md-tabs>`. Make sure if you're implementing your own `md-tab`
@@ -89,11 +81,9 @@ export class Tab extends tabBaseClass {
   private readonly assignedDefaultNodes!: Node[];
   @queryAssignedElements({slot: 'icon', flatten: true})
   private readonly assignedIcons!: HTMLElement[];
-  private readonly internals = polyfillElementInternalsAria(
-    this,
+  private readonly internals =
     // Cast needed for closure
-    (this as HTMLElement).attachInternals(),
-  );
+    (this as HTMLElement).attachInternals();
 
   constructor() {
     super();
diff --git a/tabs/internal/tabs.ts b/tabs/internal/tabs.ts
index b3d4dc2e3..290ff0fd0 100644
--- a/tabs/internal/tabs.ts
+++ b/tabs/internal/tabs.ts
@@ -9,11 +9,6 @@ import '../../divider/divider.js';
 import {html, isServer, LitElement} from 'lit';
 import {property, query, queryAssignedElements} from 'lit/decorators.js';
 
-import {
-  polyfillARIAMixin,
-  polyfillElementInternalsAria,
-} from '../../internal/aria/aria.js';
-
 import {ANIMATE_INDICATOR, Tab} from './tab.js';
 
 /**
@@ -41,10 +36,6 @@ import {ANIMATE_INDICATOR, Tab} from './tab.js';
  *
  */
 export class Tabs extends LitElement {
-  static {
-    polyfillARIAMixin(Tabs);
-  }
-
   /**
    * The tabs of this tab bar.
    */
@@ -117,11 +108,9 @@ export class Tabs extends LitElement {
     return this.tabs.find((tab) => tab.matches(':focus-within'));
   }
 
-  private readonly internals = polyfillElementInternalsAria(
-    this,
+  private readonly internals =
     // Cast needed for closure
-    (this as HTMLElement).attachInternals(),
-  );
+    (this as HTMLElement).attachInternals();
 
   constructor() {
     super();