Bug 2044655 - Force app.update.disabledForTesting to true when recommended preferences are disabled

README.md

@@ -112,7 +112,12 @@ You can pass flags or environment variables (names on the right):
 - `--android-package` — Android app package name, default `org.mozilla.firefox`. Other packages: `org.mozilla.firefox_beta` for Firefox Beta, `org.mozilla.fenix` for Firefox Nightly, `org.mozilla.fenix.debug` for Firefox Nightly Debug, `org.mozilla.geckoview_example` for geckoview (`ANDROID_PACKAGE`)
 - `--log-file` — write MCP server logs to a file instead of stderr. Useful for debugging sessions with MCP clients that hide server output. Set `DEBUG=*` to also include verbose debug logs. Example: `--log-file /tmp/firefox-mcp.log`
 
-> **Note on `--pref`:** When Firefox runs in automation, it applies [RecommendedPreferences](https://searchfox.org/firefox-main/source/remote/shared/RecommendedPreferences.sys.mjs) that modify browser behavior for testing. The `--pref` option allows overriding these defaults when needed.
+
+### Useful preferences (`--pref`)
+
+- remote.prefs.recommended=false. When Firefox runs in automation, it applies [RecommendedPreferences](https://searchfox.org/firefox-main/source/remote/shared/RecommendedPreferences.sys.mjs) that modify browser behavior for testing. Set remote.prefs.recommended to false to skip those and have a configuration closer to a regular Firefox instance.
+- remote.log.level=Trace. Enable verbose WebDriver protocol logs in Firefox. The MCP server will automatically pass the matching log level to geckodriver so both sides log at the same verbosity.
+- app.update.disabledForTesting=false. Allow Firefox to automatically download and apply updates. Note that updates may interrupt your session. Requires also setting remote.prefs.recommended=false.
 
 ### Firefox for Android
 

src/firefox/core.ts

@@ -222,6 +222,12 @@ export class FirefoxCore {
         for (const [name, value] of Object.entries(this.options.prefs)) {
           firefoxOptions.setPreference(name, value);
         }
+        if (
+          this.options.prefs['remote.prefs.recommended'] === false &&
+          !('app.update.disabledForTesting' in this.options.prefs)
+        ) {
+          firefoxOptions.setPreference('app.update.disabledForTesting', true);
+        }
       }
 
       let serviceBuilder;

tests/firefox/core-prefs.test.ts

@@ -102,6 +102,28 @@ describe('FirefoxCore prefs via firefoxOptions', () => {
     expect(mockServiceBuilderAddArguments).not.toHaveBeenCalledWith('--log', expect.anything());
   });
 
+  it('should automatically set app.update.disabledForTesting when remote.prefs.recommended is false', async () => {
+    mockSelenium();
+    const { FirefoxCore } = await import('../../src/firefox/core.js');
+    const core = new FirefoxCore({
+      headless: true,
+      prefs: { 'remote.prefs.recommended': false },
+    });
+    await core.connect();
+    expect(mockSetPreference).toHaveBeenCalledWith('app.update.disabledForTesting', true);
+  });
+
+  it('should not override app.update.disabledForTesting when explicitly set alongside remote.prefs.recommended=false', async () => {
+    mockSelenium();
+    const { FirefoxCore } = await import('../../src/firefox/core.js');
+    const core = new FirefoxCore({
+      headless: true,
+      prefs: { 'remote.prefs.recommended': false, 'app.update.disabledForTesting': false },
+    });
+    await core.connect();
+    expect(mockSetPreference).not.toHaveBeenCalledWith('app.update.disabledForTesting', true);
+  });
+
   it('should not require MOZ_REMOTE_ALLOW_SYSTEM_ACCESS', async () => {
     delete process.env.MOZ_REMOTE_ALLOW_SYSTEM_ACCESS;
     mockSelenium();