diff --git a/.github/workflows/sync-firefox-gecko.yml b/.github/workflows/sync-firefox-gecko.yml
new file mode 100644
index 0000000..ac76881
--- /dev/null
+++ b/.github/workflows/sync-firefox-gecko.yml
@@ -0,0 +1,53 @@
+name: Sync Firefox Gecko types
+
+on:
+  schedule:
+    - cron: '0 6 * * 1'
+
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  sync:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v7
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v6
+        with:
+          node-version: 24
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Generate Gecko types
+        run: npm run gecko:generate
+
+      - name: Check
+        run: npm run check
+
+      - name: Create pull request
+        uses: peter-evans/create-pull-request@v8
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          branch: automation/sync-firefox-gecko-types
+          delete-branch: true
+          commit-message: 'chore: sync Firefox Gecko types'
+          title: 'chore: sync Firefox Gecko types'
+          body: |
+            Firefox's MediaController.webidl changed.
+
+            This PR updates the generated TypeScript declarations
+            from the current Firefox main branch.
+
+            Please review the generated diff before merging.
+          labels: |
+            automated
+            dependencies
diff --git a/.gitignore b/.gitignore
index 95cc9b8..ee73310 100644
--- a/.gitignore
+++ b/.gitignore
@@ -31,3 +31,4 @@ docs/superpowers/
 *.njsproj
 *.sln
 *.sw?
+.tmp/
\ No newline at end of file
diff --git a/package-lock.json b/package-lock.json
index 017cec0..0f77417 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -15,7 +15,8 @@
         "knip": "^6.32.2",
         "oxfmt": "^0.63.0",
         "oxlint": "^1.78.0",
-        "typescript": "^7.0.2"
+        "typescript": "^7.0.2",
+        "webidl2": "^24.5.0"
       },
       "engines": {
         "node": ">=24"
@@ -3325,6 +3326,16 @@
         "node": "20 || >=22"
       }
     },
+    "node_modules/webidl2": {
+      "version": "24.5.0",
+      "resolved": "https://registry.npmjs.org/webidl2/-/webidl2-24.5.0.tgz",
+      "integrity": "sha512-fxOigKkIem1iAgQ9t4cFOP+kWEA8y6Be/uh50FpJh0FijoeeT/VMrOyJzNLUgjy0rGMEcHeReKDCqj0g9dIe9A==",
+      "dev": true,
+      "license": "W3C",
+      "engines": {
+        "node": ">= 18"
+      }
+    },
     "node_modules/wrap-ansi": {
       "version": "9.0.2",
       "resolved": "https://registry.npmjs.org/wrap-ansi/-/wrap-ansi-9.0.2.tgz",
diff --git a/package.json b/package.json
index 0da17cb..0b7d71e 100644
--- a/package.json
+++ b/package.json
@@ -29,7 +29,9 @@
     "format:check": "oxfmt --check",
     "typecheck": "tsc --noEmit",
     "typecheck:watch": "tsc --noEmit --watch",
-    "check:deps": "knip"
+    "check:deps": "knip",
+    "gecko:generate": "tsx scripts/generate-gecko-media.ts",
+    "gecko:check": "npm run gecko:generate && npm run format && git diff --exit-code -- types/gecko-media.generated.d.ts"
   },
   "devDependencies": {
     "@changesets/cli": "^3.0.0",
@@ -38,7 +40,8 @@
     "knip": "^6.32.2",
     "oxfmt": "^0.63.0",
     "oxlint": "^1.78.0",
-    "typescript": "^7.0.2"
+    "typescript": "^7.0.2",
+    "webidl2": "^24.5.0"
   },
   "engines": {
     "node": ">=24"
diff --git a/scripts/generate-gecko-media.ts b/scripts/generate-gecko-media.ts
new file mode 100644
index 0000000..c9b8456
--- /dev/null
+++ b/scripts/generate-gecko-media.ts
@@ -0,0 +1,215 @@
+import { writeFile } from 'node:fs/promises';
+import { parse } from 'webidl2';
+
+const SOURCE_URL =
+  'https://raw.githubusercontent.com/mozilla-firefox/firefox/main/dom/chrome-webidl/MediaController.webidl';
+
+const OUTPUT_FILE = 'types/gecko-media.generated.d.ts';
+
+type IDLType = {
+  idlType: string | IDLType[];
+  generic?: string;
+  union?: boolean;
+};
+
+type Attribute = {
+  type: 'attribute';
+  name: string;
+  readonly: boolean;
+  idlType: IDLType;
+};
+
+type Argument = {
+  name: string;
+  optional: boolean;
+  idlType: IDLType;
+};
+
+type Operation = {
+  type: 'operation';
+  name: string;
+  arguments: Argument[];
+  idlType: IDLType;
+};
+
+type Interface = {
+  type: 'interface';
+  name: string;
+  inheritance?: string;
+  members: Array<Attribute | Operation>;
+};
+
+type Enum = {
+  type: 'enum';
+  name: string;
+  values: Array<{ value: string }>;
+};
+
+type Namespace = {
+  type: 'namespace';
+  name: string;
+  members: Operation[];
+};
+
+type Definition = Interface | Enum | Namespace;
+
+export async function generateGeckoMedia(): Promise<string> {
+  console.log(`Fetching ${SOURCE_URL}`);
+
+  const response = await fetch(SOURCE_URL);
+
+  if (!response.ok) {
+    throw new Error(
+      `Failed to fetch WebIDL: ${response.status} ${response.statusText}`,
+    );
+  }
+
+  const source = await response.text();
+
+  if (!source.includes('interface MediaController')) {
+    throw new Error(
+      'Fetched content does not contain MediaController interface',
+    );
+  }
+
+  const definitions = parse(source) as unknown as Definition[];
+
+  console.log(`Parsed ${definitions.length} definitions`);
+
+  function tsType(type: IDLType): string {
+    if (type.union) {
+      if (!Array.isArray(type.idlType)) {
+        throw new Error('Expected union IDL type to contain an array');
+      }
+
+      return type.idlType.map(tsType).join(' | ');
+    }
+
+    if (type.generic === 'sequence') {
+      if (!Array.isArray(type.idlType) || type.idlType.length !== 1) {
+        throw new Error('Expected sequence<T>');
+      }
+
+      return `readonly ${tsType(type.idlType[0])}[]`;
+    }
+
+    if (Array.isArray(type.idlType)) {
+      throw new Error(`Unsupported IDL type: ${JSON.stringify(type)}`);
+    }
+
+    const primitiveTypes: Record<string, string> = {
+      boolean: 'boolean',
+      byte: 'number',
+      octet: 'number',
+      short: 'number',
+      'unsigned short': 'number',
+      long: 'number',
+      'unsigned long': 'number',
+      'long long': 'number',
+      'unsigned long long': 'number',
+      float: 'number',
+      'unrestricted float': 'number',
+      double: 'number',
+      'unrestricted double': 'number',
+      DOMString: 'string',
+      ByteString: 'string',
+      USVString: 'string',
+      undefined: 'void',
+      object: 'object',
+      symbol: 'symbol',
+      any: 'any',
+    };
+
+    return primitiveTypes[type.idlType] ?? type.idlType;
+  }
+
+  function renderEnum(definition: Enum): string {
+    const values = definition.values
+      .map(({ value }) => `  | ${JSON.stringify(value)}`)
+      .join('\n');
+
+    return `type ${definition.name} =\n${values};`;
+  }
+
+  function renderAttribute(member: Attribute): string {
+    const readonly = member.readonly ? 'readonly ' : '';
+
+    return `  ${readonly}${member.name}: ${tsType(member.idlType)};`;
+  }
+
+  function renderArgument(argument: Argument): string {
+    const optional = argument.optional ? '?' : '';
+
+    return `${argument.name}${optional}: ${tsType(argument.idlType)}`;
+  }
+
+  function renderOperation(member: Operation): string {
+    const args = member.arguments.map(renderArgument).join(', ');
+
+    return `  ${member.name}(${args}): ${tsType(member.idlType)};`;
+  }
+
+  function renderInterface(definition: Interface): string {
+    const inheritance = definition.inheritance
+      ? ` extends ${definition.inheritance}`
+      : '';
+
+    const members = definition.members
+      .map((member) => {
+        switch (member.type) {
+          case 'attribute':
+            return renderAttribute(member);
+
+          case 'operation':
+            return renderOperation(member);
+
+          default:
+            throw new Error(`Unsupported interface member: ${String(member)}`);
+        }
+      })
+      .join('\n');
+
+    return `interface ${definition.name}${inheritance} {\n${members}\n}`;
+  }
+
+  function renderNamespace(definition: Namespace): string {
+    const members = definition.members
+      .map((member) => {
+        const args = member.arguments.map(renderArgument).join(', ');
+
+        return `  function ${member.name}(${args}): ${tsType(member.idlType)};`;
+      })
+      .join('\n');
+
+    return `declare namespace ${definition.name} {\n${members}\n}`;
+  }
+
+  function renderDefinition(definition: Definition): string {
+    switch (definition.type) {
+      case 'enum':
+        return renderEnum(definition);
+
+      case 'interface':
+        return renderInterface(definition);
+
+      case 'namespace':
+        return renderNamespace(definition);
+
+      default:
+        throw new Error(`Unsupported WebIDL definition: ${String(definition)}`);
+    }
+  }
+
+  return [
+    '// GENERATED FILE — DO NOT EDIT',
+    `// Source: ${SOURCE_URL}`,
+    '',
+    ...definitions.flatMap((definition) => [renderDefinition(definition), '']),
+  ].join('\n');
+}
+
+const generated = await generateGeckoMedia();
+
+await writeFile(OUTPUT_FILE, generated, 'utf8');
+
+console.log(`Generated ${OUTPUT_FILE}`);
diff --git a/types/gecko-media.d.ts b/types/gecko-media.d.ts
index 2cb99cb..46d654d 100644
--- a/types/gecko-media.d.ts
+++ b/types/gecko-media.d.ts
@@ -30,67 +30,6 @@ interface PositionStateEvent extends Event {
 
 interface AudioSessionType {}
 
-/**
- * The reason a chrome caller is pausing the controller. "user" preserves the
- * existing user-initiated pause; the "system-*" values represent an
- * audio-focus loss, with "system-transient" being resumable and
- * "system-permanent" not.
- */
-type AudioFocusLossReason = 'user' | 'system-transient' | 'system-permanent';
-
-interface MediaController extends EventTarget {
-  readonly id: number;
-  readonly isActive: boolean;
-  readonly isAudible: boolean;
-  readonly isMuted: boolean;
-  readonly isPlaying: boolean;
-  readonly isAnyMediaBeingControlled: boolean;
-  readonly playbackState: MediaSessionPlaybackState;
-  readonly effectiveAudioSessionType: AudioSessionType;
-  readonly supportedKeys: readonly MediaControlKey[];
-
-  getMetadata(): MediaMetadataInit;
-
-  onactivated: EventHandler;
-  onaudiblechange: EventHandler;
-  ondeactivated: EventHandler;
-  oneffectiveaudiosessiontypechange: EventHandler;
-  onmetadatachange: EventHandler;
-  onplaybackstatechange: EventHandler;
-  onpositionstatechange: EventHandler; // Already present
-  onsupportedkeyschange: EventHandler;
-
-  focus(): void;
-  play(): void;
-  pause(reason: AudioFocusLossReason): void;
-  resume(): void;
-  stop(): void;
-  mute(): void;
-  unmute(): void;
-  prevTrack(): void;
-  nextTrack(): void;
-  seekBackward(seekOffset: number): void;
-  seekForward(seekOffset: number): void;
-  skipAd(): void;
-  seekTo(seekTime: number, fastSeek?: boolean): void;
-}
-
-type MediaControlKey =
-  | 'focus'
-  | 'play'
-  | 'pause'
-  | 'playpause'
-  | 'previoustrack'
-  | 'nexttrack'
-  | 'seekbackward'
-  | 'seekforward'
-  | 'skipad'
-  | 'seekto'
-  | 'stop'
-  | 'mute'
-  | 'unmute'
-  | 'setvolume';
-
 interface MediaControllerEventMap {
   activated: Event;
   audiblechange: Event;
diff --git a/types/gecko-media.generated.d.ts b/types/gecko-media.generated.d.ts
new file mode 100644
index 0000000..fd1477d
--- /dev/null
+++ b/types/gecko-media.generated.d.ts
@@ -0,0 +1,63 @@
+// GENERATED FILE — DO NOT EDIT
+// Source: https://raw.githubusercontent.com/mozilla-firefox/firefox/main/dom/chrome-webidl/MediaController.webidl
+
+type MediaControlKey =
+  | 'focus'
+  | 'play'
+  | 'pause'
+  | 'playpause'
+  | 'previoustrack'
+  | 'nexttrack'
+  | 'seekbackward'
+  | 'seekforward'
+  | 'skipad'
+  | 'seekto'
+  | 'stop'
+  | 'mute'
+  | 'unmute'
+  | 'setvolume';
+
+type AudioFocusLossReason = 'user' | 'system-transient' | 'system-permanent';
+
+interface MediaController extends EventTarget {
+  readonly id: number;
+  readonly isActive: boolean;
+  readonly isAudible: boolean;
+  readonly isMuted: boolean;
+  readonly isPlaying: boolean;
+  readonly isAnyMediaBeingControlled: boolean;
+  readonly playbackState: MediaSessionPlaybackState;
+  readonly effectiveAudioSessionType: AudioSessionType;
+  getMetadata(): MediaMetadataInit;
+  readonly supportedKeys: readonly MediaControlKey[];
+  onactivated: EventHandler;
+  ondeactivated: EventHandler;
+  onaudiblechange: EventHandler;
+  oneffectiveaudiosessiontypechange: EventHandler;
+  onmetadatachange: EventHandler;
+  onplaybackstatechange: EventHandler;
+  onpositionstatechange: EventHandler;
+  onsupportedkeyschange: EventHandler;
+  focus(): void;
+  play(): void;
+  pause(reason: AudioFocusLossReason): void;
+  resume(): void;
+  stop(): void;
+  mute(): void;
+  unmute(): void;
+  prevTrack(): void;
+  nextTrack(): void;
+  seekBackward(seekOffset: number): void;
+  seekForward(seekOffset: number): void;
+  skipAd(): void;
+  seekTo(seekTime: number, fastSeek?: boolean): void;
+}
+
+declare namespace MediaControlService {
+  function generateMediaControlKey(
+    aKey: MediaControlKey,
+    aSeekValue?: number,
+  ): void;
+  function getCurrentActiveMediaMetadata(): MediaMetadataInit;
+  function getCurrentMediaSessionPlaybackState(): MediaSessionPlaybackState;
+}